infinityis

The gate resistor is indeed a standard resistor; it is only called a gate resistor because of how it is used in the circuit, connected to the gate of the TRIAC or SCR. Good catch on R3, I've corrected it above to be a 180ohm resistor part number.
 
In the schematic, yes, SW2 is a TRIAC and SW3 is a SCR. 
 
R1 for the relay section is either a 330ohm resistor for an opto-driven relay coil or a 680ohm resistor for a transistor-driven relay coil (I've updated the BOM above to reflect that as well). In the schematic, SW1 is a relay that is driven by an optocoupler, whereas SW4 is a relay driven by an NPN transistor. The rationale behind which to choose depends on several factors:
 
Arguments for using optoisolator-driven relay coil
In some instances (such as the transformerless power supply configuration), the optoisolator is required because the configuration uses two voltages (3.3V for the MSP430 and 24V for the relay coil) with separate grounds. In the transformerless power suppply specifically, the 24V ground is basically tied to the positive side of the low voltage. If you try to use a transistor instead of an opto, the microcontroller would be unable to turn it on (because the microcontroller is unable to drive the base of the transistor above the 24V ground, i.e. the emitter voltage)
In other instances, someone may choose to use an opto because of noise or voltage level issues. For example, if you're driving a 12V relay coil from a $200 FPGA output pin, the optoisolator might be preferred over a transistor because if somehow the transistor gets damaged, you could expose your expensive FPGA to high voltages which can damage it, whereas the opto will likely continue to isolate electrically.
If the relay coil injects a bunch of noise into the driving circuit, you may want to isolate the ground through an opto, because a transistor precludes having isolated grounds.

Arguments for using transistor-driven relay coil
 

On the other hand, you may want a transistor because Vce (the voltage drop across the collector to the emitter) is low. At tens of milliamps (which is the relay coil current) passing through the output of the optocoupler, there is about a corresponding 1V drop across the output of the optocoupler. This means that with a 5V USB-powered circuit, the relay coil will never see the full 5V across it. The opto will create a voltage drop slightly more than 1V, leaving only 4V across the relay coil. The Omron relay I use states in the datasheet that it "must make" at 75% of the rated voltage, so as long as the relay sees more than 3.75V across the coil, the relay will turn on. However, that only leaves less than 0.25V of margin. Alternatively, with the NPN transistor, the Vce is only about 0.2V, you can still provide 4.8V to the relay coil directly, leaving plenty of margin (more than 1V of margin). Note also that if a 12V or 24V relay coil were to be used (which is a higher voltage than a USB connection provides), a 1V drop would be a lot less significant than it is for a 5V relay coil.
The CTR of optocouplers  is generally lower than the hfe (the DC current gain) of a transistor...The selected opto has a minimum CTR of 600%, which means that you can pass at least 6x the current through the output compared to what you drive through its input (internal LED). The 5V relay coil requires 72mA of current. 72mA is right at the maximum output current for the opto; beyond that you start to exceed the power rating of the opto. Looking at the datasheet for the LTV-815 (figure 5 specifically), I see that at 10mA forward current (into the internal LED), I get about 7.5x CTR, so I can draw 75mA on the output (which corresponds to the maximum collector current specified in the electro-optical characteristics table as well). That is barely enough to turn on the relay coil at 5V, but we can assume the current draw will be less because (as we already established) the opto driven relay coil will not give the full 5V anyway. So we figure the coil will actually draw 75mA * 4/5 = 60mA and we actually look ok with 10mA in. But do you really want the MSP430 to have to drive 10mA per relay? With all four relays on, 40mA is quite a bit of current (especially given that some MSP430 have a total maximum current output of 48mA...and we haven't even started counting the current drawn on MSP430 pins from LEDs, etc.). You can of course drive the opto (and LEDs) with a transistor instead, or by adding a transistor on the output of the opto (which is effectively taking the Darlington transistor pair on the output of the LTV815 yet another step). You could also sidestep this issue by spending a little more on the opto...insead of ~$0.2 per LTV815 at Mouser for 600% CTR, you could go for the ~$0.6 per PS2502-1-A at Mouser for a 2000% CTR (still with a 1V drop on the output though)...
The transistor costs less. If you want something that does the job elegantly by providing a 25x current gain when the output current is 75mA (so we only need 3mA to drive it on) and only 0.2V drop across the output, the transistor I chose is only $0.4. Less than 20% of the cost of the cheapest opto. For someone wanting to prototype a design with plans to go into production, that cost savings can make quite a difference.
 
I'd say the bottom line is that unless you require isolation for noise immunity, or because you need/have different grounds or other reasons to maintain isolation, I would certainly prefer the transistor-driven relay coil as shown for SW4 in the schematic (for a 5V coil relay, anyways) . The cost is lower, the voltage margins are better, the current required from the microcontroller is lower, and you are not susceptible to the CTR degradation of the opto over time (i.e. your long term reliability improves).
 
I can say that I have implemented both and at the very least, both options are functional. You can see this on the second page of the pictures of the boards pdf, where two have the optos and two have the transistors. (note that on the opto versions, I forgot to buy 330ohm resistors, so I just go it close enough by installing a 680ohm on both the top and bottom side of the board to get a parallel combination of 340ohms).

(sorry for the delay in responding; the kids were sick last week and there was quite a bit to respond to!)
 
Assuming you avoid the transformerless AC power supply capability of the board (which I recommend to keep things safer while still in development, and there would need to be a power budget analysis to see if it is feasible)...   You should not need to disconnect the USB from the computer, because all the high voltage traces/planes are optoisolated from the microcontroller (and thus from any USB connected devices as well). I mention that because I occasionally found it useful to keep it connected for debugging purposes. Also, if you disconnect the USB from the computer, then prior to step six you will need to plug in a USB charger/power supply to the Launchpad and power strip.   In my testing, IProtoPowerSwitch Demo Programs.zip
Schematic ProtoPowerSwitchBoard v8.pdf
AssemblyDrawing ProtoPowerSwitchBoard v8.pdf

(sorry for the delay in responding; the kids were sick last week and there was quite a bit to respond to!)
 
Assuming you avoid the transformerless AC power supply capability of the board (which I recommend to keep things safer while still in development, and there would need to be a power budget analysis to see if it is feasible)...   You should not need to disconnect the USB from the computer, because all the high voltage traces/planes are optoisolated from the microcontroller (and thus from any USB connected devices as well). I mention that because I occasionally found it useful to keep it connected for debugging purposes. Also, if you disconnect the USB from the computer, then prior to step six you will need to plug in a USB charger/power supply to the Launchpad and power strip.   In my testing, IProtoPowerSwitch Demo Programs.zip
Schematic ProtoPowerSwitchBoard v8.pdf
AssemblyDrawing ProtoPowerSwitchBoard v8.pdf

cubeberg, I've also been looking at using 5V from the Launchpad USB connection, and I think I've found a reasonably good way to do that and simultaneously support the 40 pin Launchpads (C2000, Stellaris).
 
If you have room, include pins for a 40 pin launchpad. One of the "new" pins (not found on a 20 pin LP) is 5V directly from the USB, at least for the C2000 Launchpad (pin 1 of J5). If someone wants to interface the boosterpack to a 40 pin launchpad, the 5V connection is made automatically, and if someone want to interface the boosterpack to a 20 pin launchpad (like the MSP430), TI was gracious enough to provide that 5V through-hole near the USB connector, so the user simply has to buy a short male/female jumper wire, cut it in half, solder the cut ends into the LP (the thru hole near the USB) and BP (pin 1 of J5), and then you have a convenient, optional 5V jumper.

The new boards are in! Hopefully I can find some time to solder it up soon and verify the functionality. They were ordered from Iteadstudio, which was actually a better deal than Seeedstudio for this size board, plus it included 100% etest instead of 50%, and they threw in an extra board when they shipped them (final qty: 11). The build quality looks quite nice. The only problem I've seen so far is that I accidentally made a few of my vias too large so they didn't tent properly. Thus, one via doesn't meet HV clearance requirements so I may have to conformal coat that via.
 
In the meantime I've started putting together some documentation describing the functionality, configuration options, etc. since there are so many different ways this thing can be put together (including using it as a basic Relay, SCR, and/or TRIAC board wherein the Launchpad itself is isolated from the mains)
 

I've had the parts soldered in for awhile now, but it's taken a bit to get up to speed with the code. To do phase angle-controlled firing of the TRIAC/SCR meant learning how to use the TimerA and all, so with that done, I was able to test the hardware today. I've got it all working now, but the board will need one more revision to work out a few small issues, including:
 

-Swap pins on the LDO. I changed to a TO92 for this board and managed to mix up two of the pins.
-Swap pins for the TRIAC/SCR. I had MT1 and MT2 mixed up for the TRIAC and anode/cathode mixed up for the SCR, such that it would take more gate current than needed to turn them on. For both this and the LDO issues, I've just worked around it for now by bending some pins.
-Fix LED assignments. Because the zero-voltage detection was a last-minute (but useful) addition to the design, when I was reassigning MSP430 nets, I didn't change the LED nets at the same time, so one of them is tied to the zero current detect input pin, where it of no use.
-Skip P1.3 for output control, so that the built-in button on the Launchpad is freed up for use as an input.

 
Other changes are either component swaps (e.g. using a 39k pulldown on the zero-volt detect worked, whereas the 660k I designed in was too weak to do any zero-voltage detection at all) or they are minor changes I'm considering, such as:
 


-Allow separation of the 3.3V and 24V regions via jumper. This provides the ability to (for example) use a common isolated wall-wart or USB power source to drive both the MSP430 and lower voltage, higher current relay coils, essentially making for a "normal" relay Boosterpack
-Possibly add holes in the corners for mounting...?
-Ensure adequate keepouts for compatibility with the second set of pins for the 40pin C2000 Launchpad
-Switch to a more standardized relay footprint; the only reason I picked the one I did was because of a typo in Mouser's part spec that made me think the coil current was lower than it actually is.

 
Despite of all those small changes I need to make for the next revision, it was quite satisfying to see the microcontroller gradually dim a lightbulb by adjusting the phase angle triggering of the SCR and TRIAC.

The new boards are in! Hopefully I can find some time to solder it up soon and verify the functionality. They were ordered from Iteadstudio, which was actually a better deal than Seeedstudio for this size board, plus it included 100% etest instead of 50%, and they threw in an extra board when they shipped them (final qty: 11). The build quality looks quite nice. The only problem I've seen so far is that I accidentally made a few of my vias too large so they didn't tent properly. Thus, one via doesn't meet HV clearance requirements so I may have to conformal coat that via.
 
In the meantime I've started putting together some documentation describing the functionality, configuration options, etc. since there are so many different ways this thing can be put together (including using it as a basic Relay, SCR, and/or TRIAC board wherein the Launchpad itself is isolated from the mains)
 

The MSP430 has a 1.5 or 2.5 volt (software selectable) bandgap reference that can be output to external circuits as well as being used internally. The 2.5V ref is stable from a supply voltage of 2.9 to 3.6V.
 
The MCP3208 does not do concurrent sampling, so even split phase is pushing the limits.
 
The schematic does not portray the PCB layout with any significant detail. The PCB would have split analog and digital ground planes and/or star grounding with the digital and analog grounds joined at a single place. The input channels would be guarded by agnd.

Here are two design proposals. Up to 6 of each can be stacked to increase channel count.
 
The first uses a 12 bit ADC and has 2 channels that can be used for voltage or current and 5 channels that are current only. This could be used for single or split phase applications. Accuracy would be poor at low load due to limited ADC resolution.
 
A 2.5 V reference voltage is supplied by the MSP430 and buffered by IC1A. The buffered reference is used by the ADC and also divided by 2 and buffered by IC1B to create a bias for the sensors. The first ADC channel reads the bias voltage so it can be subtracted from the other 7 channels and produce a signed result representing voltages above and below 'zero'.
 
Each input has a simple passive first order low pass filter to reduce aliasing. A second or higher order filter would be better, but require many more components.
 

 
The second uses a 24 bit (max) ADC and has 3 channels that can be used for voltage or current and 3 channels that are current only. It could be used for single, split, or 3 phase applications. Accuracy would probably be limited by the voltage and current transformers used. It could approach 'utility grade' precision with careful hardware and firmware design.
 
Each input is balanced and ground referenced. TP or STP cable would be used to minimize pickup of unwanted signals in the wiring. Passive first order low pass filter to reduce aliasing.
 
The MCP3903 ADC is made for power monitoring applications and has hardware assist for phase lead/lag compensation. This would be a SMD design to ensure maximum performance - ground planes and guarding are critical for high resolution measurement.
 

I've been making some updates/changes to the AC-powered relay/SCR/TRIAC board, and I'm getting close to sending it out for fab. Some of the changes include:
 
- Added LEDs to show when the relay/SCR/TRIAC signals are turned on.
- Added zero voltage detection capability (still need to add a filter cap). I opted for an opto because the AC input ones (that use a back-to-back LED internally) eliminated the need for a dedicated bridge rectifier. This also ensure that if desired, the board can still be safely powered by an isolated power supply (e.g. wall wart) and still control AC power through the switching device, even with phase angle controlled firing for the SRCs/TRIACs
- Added terminals to provide access to unused pins (caution! shock hazard when board is powered by AC power!)
- Improved layout to ensure sufficient trace widths for high currents and sufficient clearance for elevations up to 3050m without conformal coating
 
I may still renumber the connectors to make it easier to track (e.g. P11 maps to J1, P12 to J2, etc).
The size is presently about 2" by 4".

Schematic AC Powered relay SCR TRIAC board v6.pdf
 
 
As always, feedback and comments are welcome.
 
Thanks,
David

I've been making some updates/changes to the AC-powered relay/SCR/TRIAC board, and I'm getting close to sending it out for fab. Some of the changes include:
 
- Added LEDs to show when the relay/SCR/TRIAC signals are turned on.
- Added zero voltage detection capability (still need to add a filter cap). I opted for an opto because the AC input ones (that use a back-to-back LED internally) eliminated the need for a dedicated bridge rectifier. This also ensure that if desired, the board can still be safely powered by an isolated power supply (e.g. wall wart) and still control AC power through the switching device, even with phase angle controlled firing for the SRCs/TRIACs
- Added terminals to provide access to unused pins (caution! shock hazard when board is powered by AC power!)
- Improved layout to ensure sufficient trace widths for high currents and sufficient clearance for elevations up to 3050m without conformal coating
 
I may still renumber the connectors to make it easier to track (e.g. P11 maps to J1, P12 to J2, etc).
The size is presently about 2" by 4".

Schematic AC Powered relay SCR TRIAC board v6.pdf
 
 
As always, feedback and comments are welcome.
 
Thanks,
David

A small capacitor from the live wire, followed by a low pass filter (simple RC) to clean up the HF noise is usually enough when we talk of interfacing to CMOS MCUs. If you want to play uber-safe, then a couple 1N914 to ground and VCC will take care of excesses.

Looking good. Would having an LED be helpful?
Also, if you need $10 for sponsoring your first batch of boards, let me know.

I am using a thermistor in mine. This one
 
http://uk.farnell.com/epcos/b57560g104f ... tt=3878697
 
It is the same as I use in my 3d printers, and takes heat up to 300C. I could have used a cheaper one for water, but I want to use the same for avreflow oven or soldering plate. It has to be enclosed if in water, but works well. The resistance change is not linear though. 3d printer sites hav conversion tables. It is a very simple circuit. You just need a resistor and an analog input on the mcu.
 
Thanks for the project link. I am planning to isolate the thermistor. Its necessary for it to work properly in water.
 
Thermocouples are nice too of course, but quite expensive in comparison.
 
My project will connect into the middle of a power extension cord, so I can connect any 230v device that can take being turned on or off. I will use this enclosure to isolate the board:
 
http://uk.farnell.com/multicomp/mcrp106 ... tt=1520406
 
Sorry for interfering on the thread, but I guess this might be useful for someone wanting to use your board.

The cc2500 is a tranceiver chip. Connect it to an mcu. The mcu implements the protocol, which could be zigbee or a free open sourcealternative like simpliciTI. Zigbee with cc2500 would require you having access to a zigbee stack, which is relative,y heavy. TI have a zigbee stack, but I have not looked into it. I think it is more common to use more specific Zigbee modules. I could find out for you if you need sigbee.
 
More info on TI zigbee here http://www.ti.com/tool/z-stack&DCMP=HPA ... OT+z-stack
 
 
Btw, I am trying for a sous vide project (controlled water heater). An isolated supply is required I think. Advice is welcome.

It's scary, yes.. but don't let this stop you. I'm more afraid to plug the thing the other way round on an LP.. even on the current boosterpacks. :!!!:
 
keep us updated on your progress. Coupling this with the CC2500 really opens up boundaries..especially into home automation.

Larsie, thanks for the link to an enclosure; it should work well for applications like ours provided that the chassis/safety ground exists and care is taken to ensure the metal of the enclosure is tied only to the chassis/safety ground. If the chassis/safety ground wire is not provided or available, a plastic enclosure should be used instead because it is possible for a loose wire internally to contact a metal housing and energize it, whereas a plastic enclosure (like laptop power supply) is insulative and cannot become energized even if a wire comes loose inside. (Edit: nevermind, just realized the description states the enclosure is made out of ABS plastic and not metal, so no need to worry about grounding the enclosure)
 
And yes, 15-30mA can kill. Again, I recommend plugging into a GFCI outlet when working on something non-isolated from the mains; even though you can still get killed by the 120V, you do gain protection from accidental shorts to other objects/surfaces tied to the earth/chassis/safety ground.
 
Jim
Not to be pedantic, but since it affects safety....techically the distinction is not AC vs. DC but isolated vs. non-isolated. A device which provides galvanic isolation (i.e. high impedance) from the mains can safely connect any one (but only one) of it's output wires to the AC chassis/safety ground. For example, if you take the AC mains power and run it through an isolation transformer, then it safe to tie one end of the output to the chassis/safety ground. Same goes for a DC power supply with an isolated output. However, the circuit I use for the transformerless power supply booster pack cannot have anything tied to safety/chassis ground even though it is DC because there is no isolation from the mains.
 
Just to restate: isolation from the mains is what matters. The chassis ground can be used as a reference for any isolated AC or DC voltages (e.g. AC isolation transformer, DC isolated power supplies, batteries, etc). Anything that is unable "complete the circuit" to send current through the chassis/safety ground during normal operation is ok.

Larsie, thanks for the link to an enclosure; it should work well for applications like ours provided that the chassis/safety ground exists and care is taken to ensure the metal of the enclosure is tied only to the chassis/safety ground. If the chassis/safety ground wire is not provided or available, a plastic enclosure should be used instead because it is possible for a loose wire internally to contact a metal housing and energize it, whereas a plastic enclosure (like laptop power supply) is insulative and cannot become energized even if a wire comes loose inside. (Edit: nevermind, just realized the description states the enclosure is made out of ABS plastic and not metal, so no need to worry about grounding the enclosure)
 
And yes, 15-30mA can kill. Again, I recommend plugging into a GFCI outlet when working on something non-isolated from the mains; even though you can still get killed by the 120V, you do gain protection from accidental shorts to other objects/surfaces tied to the earth/chassis/safety ground.
 
Jim
Not to be pedantic, but since it affects safety....techically the distinction is not AC vs. DC but isolated vs. non-isolated. A device which provides galvanic isolation (i.e. high impedance) from the mains can safely connect any one (but only one) of it's output wires to the AC chassis/safety ground. For example, if you take the AC mains power and run it through an isolation transformer, then it safe to tie one end of the output to the chassis/safety ground. Same goes for a DC power supply with an isolated output. However, the circuit I use for the transformerless power supply booster pack cannot have anything tied to safety/chassis ground even though it is DC because there is no isolation from the mains.
 
Just to restate: isolation from the mains is what matters. The chassis ground can be used as a reference for any isolated AC or DC voltages (e.g. AC isolation transformer, DC isolated power supplies, batteries, etc). Anything that is unable "complete the circuit" to send current through the chassis/safety ground during normal operation is ok.

Actually, thermocouples generate a small voltage due to the dissimilar metals. So instead of a resistor divider, you just need measure it directly. Well, almost directly...as shown in the TI link I posted above, you want to put resistors in series with the lines and couple them with capacitors. The reason you'd need/want to do this is because even though the thermocouple generates a voltage, it cannot source much current. The ADC draws a small amount of current to measure the voltage, but it is more current than the thermocouple can source. Steady state, the capacitor voltage will settle at the thermocouple voltage. With capacitors near the ADC, the current used to sample comes out of the capacitors which are resting at the thermocouple voltage. The resistors between the capacitors and the thermocouple serve to limit (actually almost completely eliminates) the surge of ADC sampling current which comes from the thermocouple. And thus we have a basic low-pass RC filter.
 
Other temperature sensing elements (such as an RTD, resistive temperature detector) do have a resistance that varies with temperature, so you can use a resistor divider circuit to simply measure the voltage. There are two things to be aware of for high precision temperature measurements with RTDs, however. First, you will want to use two wires to apply the voltage across the resistance and two separate wires connected very close to the RTD to measure the voltage (such that the sensing lines don't have to carry much/any current and thus you eliminate resistance contributions in the measurement lines). Second, the act of measuring continuously (forcing continuous DC current through the RTD) actually causes the RTD to heat up slightly, affecting the measurement; this can be mitigated through some clever low-current AC coupling as shown here.

Just FYI, you may be able to get it a tiny bit cheaper here. Shipping may be higher though for all I know.

NOTE: this BoosterPack uses high voltage (120V) AC power which is dangerous and can be fatal if not handled/packaged properly

I created my first BoosterPack for the MSP430: an AC-powered AC relay. This BoosterPack takes in 120V AC and uses a transformerless power supply to cheaply/compactly create low DC voltage, which is then used to power the MSP430 Launchpad and drive a 7A relay. There is enough overhead in the currently design to power at least 3 relays, but it only has one designed in at the moment to make for the smallest/cheapest proof of concept. The board provides approximately 30mA at 3.3VDC and 30mA at 24VDC (note: the 3.3V VCC is wired directly to the 24V GND).

A video of it operating is
, pictures and schematic are here.


There are some minor changes/fixes in the works for the next version but I thought I'd go ahead and open it up for comments/feedback.

-The board was set up to accommodate either a 7A or a 15A relay, but the overlapping drill hits required for the relay didn't come out right so this one only works with the 7A relay. Also, if the 7A relay is unpopulated, you can still use the coil's thru-holes as a controllable 24V source (on/off).
-One of the AC connector terminals was bigger than the datasheet stated so it currently leans to the side a bit.
-The plan was to have a 6V+ output which passed through a LDO that provided a steady 3.3VDC. However, the LDO doesn't regulate very well without a minimum load, and MSP430 itself doesn't draw enough power by itself to meet that minimum requirement; it only works right when the top portion of the Launchpad is powered by it as well. I'll probably be changing the LDO in the future to one which does not require as much load current. fixed: it was a just board layout issue
-I am currently drawing 24V and 3.3V separately (without common ground); I have considered with the idea of just drawing the 24V and regulating it down to 3.3V levels to get even more current at 3.3V. This would also allow the same board to be used in both AC-powered and non-AC-powered applications (where all you want is an AC relay board).
-I placed the DC caps on the back of the board; unfortunately right where the crystal oscillator is. They'll be moved the next time around.
-Would something like this work better as its own board (with the MSP430 on the board itself, not as a BoosterPack)?
-There is a tradeoff regarding more current vs. being referenced to neutral; this board uses a bridge rectifier to get extra current. A neutral-referenced version would be needed to work with SCRs/TRIACs instead of relays.
-Is the general preference for 3.3V or 1.8V operation of the MSP430? Are there pins that are recommended or discouraged for use in driving the relays?
-Several "tall" components are used on the board; would it be best to move them out of the Launchpad area entirely to allow other BoosterPacks to be stacked, or is something like this more acceptable to always have as the top of the stack?


If there is any interest in this type of BoosterPack (or a customized variant), please let me know what you'd like to see. I should mention that in general, if/when sold in small quantities, it would be as a kit with the AC line cap and/or relay(s) not installed to minimize liability.

NOTE: this BoosterPack uses high voltage (120V) AC power which is dangerous and can be fatal if not handled/packaged properly

I created my first BoosterPack for the MSP430: an AC-powered AC relay. This BoosterPack takes in 120V AC and uses a transformerless power supply to cheaply/compactly create low DC voltage, which is then used to power the MSP430 Launchpad and drive a 7A relay. There is enough overhead in the currently design to power at least 3 relays, but it only has one designed in at the moment to make for the smallest/cheapest proof of concept. The board provides approximately 30mA at 3.3VDC and 30mA at 24VDC (note: the 3.3V VCC is wired directly to the 24V GND).

A video of it operating is
, pictures and schematic are here.


There are some minor changes/fixes in the works for the next version but I thought I'd go ahead and open it up for comments/feedback.

-The board was set up to accommodate either a 7A or a 15A relay, but the overlapping drill hits required for the relay didn't come out right so this one only works with the 7A relay. Also, if the 7A relay is unpopulated, you can still use the coil's thru-holes as a controllable 24V source (on/off).
-One of the AC connector terminals was bigger than the datasheet stated so it currently leans to the side a bit.
-The plan was to have a 6V+ output which passed through a LDO that provided a steady 3.3VDC. However, the LDO doesn't regulate very well without a minimum load, and MSP430 itself doesn't draw enough power by itself to meet that minimum requirement; it only works right when the top portion of the Launchpad is powered by it as well. I'll probably be changing the LDO in the future to one which does not require as much load current. fixed: it was a just board layout issue
-I am currently drawing 24V and 3.3V separately (without common ground); I have considered with the idea of just drawing the 24V and regulating it down to 3.3V levels to get even more current at 3.3V. This would also allow the same board to be used in both AC-powered and non-AC-powered applications (where all you want is an AC relay board).
-I placed the DC caps on the back of the board; unfortunately right where the crystal oscillator is. They'll be moved the next time around.
-Would something like this work better as its own board (with the MSP430 on the board itself, not as a BoosterPack)?
-There is a tradeoff regarding more current vs. being referenced to neutral; this board uses a bridge rectifier to get extra current. A neutral-referenced version would be needed to work with SCRs/TRIACs instead of relays.
-Is the general preference for 3.3V or 1.8V operation of the MSP430? Are there pins that are recommended or discouraged for use in driving the relays?
-Several "tall" components are used on the board; would it be best to move them out of the Launchpad area entirely to allow other BoosterPacks to be stacked, or is something like this more acceptable to always have as the top of the stack?


If there is any interest in this type of BoosterPack (or a customized variant), please let me know what you'd like to see. I should mention that in general, if/when sold in small quantities, it would be as a kit with the AC line cap and/or relay(s) not installed to minimize liability.

NOTE: this BoosterPack uses high voltage (120V) AC power which is dangerous and can be fatal if not handled/packaged properly

I created my first BoosterPack for the MSP430: an AC-powered AC relay. This BoosterPack takes in 120V AC and uses a transformerless power supply to cheaply/compactly create low DC voltage, which is then used to power the MSP430 Launchpad and drive a 7A relay. There is enough overhead in the currently design to power at least 3 relays, but it only has one designed in at the moment to make for the smallest/cheapest proof of concept. The board provides approximately 30mA at 3.3VDC and 30mA at 24VDC (note: the 3.3V VCC is wired directly to the 24V GND).

A video of it operating is
, pictures and schematic are here.


There are some minor changes/fixes in the works for the next version but I thought I'd go ahead and open it up for comments/feedback.

-The board was set up to accommodate either a 7A or a 15A relay, but the overlapping drill hits required for the relay didn't come out right so this one only works with the 7A relay. Also, if the 7A relay is unpopulated, you can still use the coil's thru-holes as a controllable 24V source (on/off).
-One of the AC connector terminals was bigger than the datasheet stated so it currently leans to the side a bit.
-The plan was to have a 6V+ output which passed through a LDO that provided a steady 3.3VDC. However, the LDO doesn't regulate very well without a minimum load, and MSP430 itself doesn't draw enough power by itself to meet that minimum requirement; it only works right when the top portion of the Launchpad is powered by it as well. I'll probably be changing the LDO in the future to one which does not require as much load current. fixed: it was a just board layout issue
-I am currently drawing 24V and 3.3V separately (without common ground); I have considered with the idea of just drawing the 24V and regulating it down to 3.3V levels to get even more current at 3.3V. This would also allow the same board to be used in both AC-powered and non-AC-powered applications (where all you want is an AC relay board).
-I placed the DC caps on the back of the board; unfortunately right where the crystal oscillator is. They'll be moved the next time around.
-Would something like this work better as its own board (with the MSP430 on the board itself, not as a BoosterPack)?
-There is a tradeoff regarding more current vs. being referenced to neutral; this board uses a bridge rectifier to get extra current. A neutral-referenced version would be needed to work with SCRs/TRIACs instead of relays.
-Is the general preference for 3.3V or 1.8V operation of the MSP430? Are there pins that are recommended or discouraged for use in driving the relays?
-Several "tall" components are used on the board; would it be best to move them out of the Launchpad area entirely to allow other BoosterPacks to be stacked, or is something like this more acceptable to always have as the top of the stack?


If there is any interest in this type of BoosterPack (or a customized variant), please let me know what you'd like to see. I should mention that in general, if/when sold in small quantities, it would be as a kit with the AC line cap and/or relay(s) not installed to minimize liability.