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SPI with Power Booster


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In wanting to make a simple Booster Pack for my WS2801 Array Binary Clock (seen here http://www.43oh.com/forum/viewtopic.php?f=9&t=1855#p13002), I've made a very simple Booster Pack for powering the Launchpad with a 9V battery or a wall-wart with SPI connections available on headers. It includes power supply, 3 buttons, and 1 potentiometer. The inputs are jumper selectable with hardware pullups for the buttons.

 

Basically, for the schematic, I 'm borrowing RobG's Booster Pack tip (http://www.43oh.com/forum/viewtopic.php?f=30&t=1844) for making SPI connections. I used his recommended method for using UCSI_A, UCSI_B and USI. The SPI connection is brought out to a 5 pin header for making connections with the WS2801 Array or other SPI devices.

 

After searching out power supply ideas, this is the simplest I could find that would provide enough power for the LP as well as the WS2801 array. It is based around a LM317D2TR4G. If you see anything that should be reconsidered, please let me know. I was sure if another diode is needed between the power supply output and the LP's input.

 

Anyone have tips or links on heatsink consideration?

 

If all looks good, I'll start the board layout and maybe make a prototype in the garage over the next few days.

 

[attachment=0]power_spi_booster.png[/attachment]

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I agree with bluehash, but you could make the pad modular: overlap a screw terminal pad with a barrel jack pad, you can pick up the terminals from radio shack so you could give people the option .. i think they have board mountable female jacks too.. it'd be worth looking into making it compatible with those (i always like to require less initially, and make things buy able locally)

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Thanks guys. As soon as I read bluehash's response, I thought about adding both adapters. Instead of having them overlap, I'm going to make them side by side so both options are available. Thought about adding a mini USB but that defeats the purpose of using the LM317D2TR4G for more current.

 

The WS2801 Array is going to draw a lot more current than the LP will. Should I add a diode between the LP and the power supply output?

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I don't know. Having two independent power sources is a recipe for trouble in my opinion. Even if you have a blocking diode in the circuit.

 

Is there a way to power the LP with the same power source as the LEDs? This would let the regulators take care of the problem.

 

Think of it as a power supply waterfall: 9V -> 5V -> 3V

Each regulator will be a check point on the irrigation canal. No flooding.

 

Alternatively, whip an msp430 onto the board you're designing. Once you do that, your power sharing issues disappear.

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Having two independent power sources is a recipe for trouble in my opinion.

 

There will only be one power source. Having two adapters on the board would a one or the other situation. According to the Launchpad's User manual, an external power source can supply Vcc but you must remove the Vcc jumper at J3. I've already tested with another power supply and it seems to work great. Just wasn't sure if the LP needed some extra protection.

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it's a LaunchPad-LaunchPad

 

Ha, yeah I guess it is. Mostly, I just wanted to be able to power a LP with a wall-wart. Needed the SPI breakouts for the RGB Binary Clock I'm building.

 

For the power side of things, the board layout keeps all the components at the top of the LP away from any pins other than Vcc and GND. Making it somewhat modular to use with other Boosters too.

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