Jump to content
Sign in to follow this  
thenutbunny

Advice about a water temperature controller

Recommended Posts

I am planning to build a msp430 based water temperature controller to test my wits in control theory, and wanted to share my design with you guys to and learn what you are thinking about it. I actually don't have any problems in the control theory or software side, but the power side is making me worry since i have absolutely o experience in power electronics :).Below is my functional diagram, i want it to be pretty awesome so i added a lot of unnecessary functionality to it, like touch lcd to configure target temp. and control coefficients on the fly, usb connection to connect it to a desktop app. i wrote or possibly MATLAB, vibration motor to circulate the water for even heating and yada yada yada.

functionaldiagramdraftv.png

 

And if we come to questions in my head:

1) I plan to use a bigger msp430, possible msp430f5xxx series to be able to implement all the features i want and leave room for

future extensions. I think i can use my Launchpad to flash and debug a msp430f5xxx that supports spybiwire, am I correct?

2) I looked but failed to find a reference design for a barebones msp430f5xxx circuit, i'm thinking about looking at the circuit

diagrams of development boards, but i want to know if there is a document about it that i couldn't find.

3) I'm planning to use a 220V AC Heater(which i will probably salvage from an electric kettle), and to control it, create a dimmer

circuit since the load will be resistive it won't create any problems, am i right?

4) I will probably get all my power from a wall plug, will you recommend any converter to power all the non-heater parts(500-600 mAmps will be enough i guess.), preferably something not too expensive and i can buy. I don't want to fiddle a lot with power, I am an electronics guy, beyond 12 volts is beyond my interest.

 

I will of course keep the community informed about my process, i expect to finish it in 4-5 weeks maybe a little longer.

Share this post


Link to post
Share on other sites

3) I'm planning to use a 220V AC Heater(which i will probably salvage from an electric kettle), and to control it, create a dimmer

circuit since the load will be resistive it won't create any problems, am i right?

4) I will probably get all my power from a wall plug, will you recommend any converter to power all the non-heater parts(500-600 mAmps will be enough i guess.), preferably something not too expensive and i can buy. I don't want to fiddle a lot with power, I am an electronics guy, beyond 12 volts is beyond my interest.

 

First of all, be very careful, you are dealing here with high voltage, make sure your circuit is properly grounded and isolated.

Dimmer circuit will be perfect for the heater. I would use opto-triac to control power triac, because opto-triacs will isolate your circuit and usually come with built-in zero crossing detector, one less thing to worry about.

Usually, circuits like this get their Vcc from line power, lowering it using a resistor and zener or regulator. Since you want to do some fancy stuff like USB connection, separate supply is the way to go. You can probably pick up cheap 5V regulated supply or salvage one from an old phone or something, or get unregulated one and just add a 5V or 3.3V regulator (http://www.sparkfun.com/products/526)

Share this post


Link to post
Share on other sites

3) I'm planning to use a 220V AC Heater(which i will probably salvage from an electric kettle), and to control it, create a dimmer

circuit since the load will be resistive it won't create any problems, am i right?

4) I will probably get all my power from a wall plug, will you recommend any converter to power all the non-heater parts(500-600 mAmps will be enough i guess.), preferably something not too expensive and i can buy. I don't want to fiddle a lot with power, I am an electronics guy, beyond 12 volts is beyond my interest.

 

First of all, be very careful, you are dealing here with high voltage, make sure your circuit is properly grounded and isolated.

Dimmer circuit will be perfect for the heater. I would use opto-triac to control power triac, because opto-triacs will isolate your circuit and usually come with built-in zero crossing detector, one less thing to worry about.

Usually, circuits like this get their Vcc from line power, lowering it using a resistor and zener or regulator. Since you want to do some fancy stuff like USB connection, separate supply is the way to go. You can probably pick up cheap 5V regulated supply or salvage one from an old phone or something, or get unregulated one and just add a 5V or 3.3V regulator (http://www.sparkfun.com/products/526)

Thanks for the answer, I think I'm going to use an old cellphone adapter. And insert the glcd later since its a tad bit on the expensive side.

Share this post


Link to post
Share on other sites

I am considering to use F5xx/F6xx with on-chip USB (that rules out F54xx). I could not find any experimental board. I am ordering samples of F5510IPTR and intend to hand-solder it.

 

Any suggestions?

Share this post


Link to post
Share on other sites
I am considering to use F5xx/F6xx with on-chip USB (that rules out F54xx). I could not find any experimental board. I am ordering samples of F5510IPTR and intend to hand-solder it.

 

Any suggestions?

 

You can solder it with a fine tip iron, its not as hard as it seems, if not you might try to get a lqfp zif socket but those guys are a little hard to get where i live.

Share this post


Link to post
Share on other sites

Thanks.

 

Yes, that is why I picked MSP430F5510IPTR. It has 48 pins sticking out of the plastic. Other F5xx/6xx chips have more pins and often have pins or "balls" underneath the plastic.

 

Which F5xx/F6xx chip are you considering?

Share this post


Link to post
Share on other sites

Hey Everyone,

 

Just thought I'd put my 2 cents in. I love the 55xx series, and have used 2 of them so far (the 5528, 5524, and soon to be 5510). The on board USB is a pain to get working to say the least, and I have only managed to get about 450 kbps for speed, which is a bit frustrating. I have been using the UART with an FTDI chip since I can easily exceed 1M baud with it.

 

As far as doing other things with the chips (non-usb) its just as straight forward as the other MSP430 chips. There are code examples on TI's website which show how to use the peripherals (my favorite is the hardware multiplier). For a basic circuit check out the target boards TI has for sale, they have the schematics posted online.

 

Also, for a development board for the 55xx devices, TI does sell a board with a nice socket for the 55xx boards (they sell a bunch for different package sizes too). They are a bit expensive though. I am currently working on making a small development board for the 5510 which I would sell. The board is basically ready but I cannot find someone who has the right package in stock (since I cannot sell boards with samples on them). The boards came out real nice though! Lots of cool features. Lol.

 

One last thing, you can definitely program the 55xx chips with the LaunchPad, I had been doing it for months and it works great.

Share this post


Link to post
Share on other sites

OCY,

 

The IPTR package should fit just fine. Currently the second wave of prototypes are being manufactured, so I should get the boards and be able to test them in 2 or 3 weeks. There should be a few extra unpopulated boards left over from this upcoming batch. If you would like I could email you when the boards come in?

 

NJC

Share this post


Link to post
Share on other sites

NJC,

The IPTR package should fit just fine. Currently the second wave of prototypes are being manufactured, so I should get the boards and be able to test them in 2 or 3 weeks. There should be a few extra unpopulated boards left over from this upcoming batch. If you would like I could email you when the boards come in?

Thank you. And yes. please do.

--OCY

old_ cow_ yellow at yahoo com

Share this post


Link to post
Share on other sites

This thread was left alone for a while because i was i little more busy than i expected but here are what i did on the time passed:

 

1-) I gave up from fancy but unnecessary stuff like touch lcd(whats bad about character lcds and 2 buttons :) ), so i ditched 5XXX series and started designing a board with F2274, i almost finished it and hopefully post it soon to hear what everyone thinks.

 

2-) I also decided not to use a dimmer circuit because since the system response is so slow that won't really provide any real advantage. Instead i will just use a relay to open and close the controller with low frequency pwm(somewhere about 1hz). At that point i will point a question:

I am driving the relay with an npn transistor and a diode, standard stuff but I wonder if i will need a optocoupler to prevent mains wreaking havoc in my precious circuit. I can't understand the power-electronics stuff but since my load is resistive i think i won't need an optocoupler but I want to hear opinions. Also i will want an optocoupler recommendation to use on my board, since I never used those little buggers.

 

Thats all for now, seems like I will be starting on my software soon. Also thanks to everyone contributed to and will contribute to thread.

 

Edit: I wanted to add that relay circuit and controller will be on seperate boards/enclosures but they will be connected electrically anyway.

Share this post


Link to post
Share on other sites

Hello,

 

I think you should consider a SCR or some kind of solid-state switch instead of a electromechanical relay. Do you have data for life expectancy of such a device if you make-and-break at the rate of once per second?

 

-- OCY

Share this post


Link to post
Share on other sites
Hello,

 

I think you should consider a SCR or some kind of solid-state switch instead of a electromechanical relay. Do you have data for life expectancy of such a device if you make-and-break at the rate of once per second?

 

-- OCY

 

I don't, and I am not expecting the answer to be long :)

I actually never measured how much current do I need and assumed much, and SSR s with much load current are pretty expensive, but it seems like i should measure my load asap :)

Share this post


Link to post
Share on other sites

OCY is right, mechanical relay, besides being loud, will also cause interference and will require more current to drive it. Solid state is a good idea since you can probably find one with zero crossing detection, but you will also pay more for what's basically a triac-in-a-box.

You can get 25A/600V triac (Q6025R6, BTA24-600, BTA26-600) for less than $2 and coupler with zero crossing detection (MOC3041) for less than $1 (at futurlec.com for example.)

Oh, and you can always connect few triacs in parallel.

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Sign in to follow this  

×
×
  • Create New...