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Author Topic: Easypic add on board project  (Read 1616 times)
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Wizpic
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« on: March 26, 2010, 05:06:25 17:06 »

Recently I wanted to measure the voltage of one of my PSUíS, Normally I knock it up on Vero-board or try and throw it together only to give up half through due to the fact that Iím not 100% happy with the reading I obtain, Like not been accurate enough compared to my multi-meter or stable enough, I know it might be asking too much from a 10bit old pic,
I did think about adding a 12-24bit A/D converter chip but they add more costís to the project plus itís writing the code (which is not a problem), I also thought about just adding a resistor divider but I thought by using an op-amp it actís has a buffer which is better I think.
So I decided to design a add on board for the Easypic board to get it right, Looked through my junk box and found the LMC660 op-amp which is a single supply/ rail to tail so I thought that will do I simulated it in ISIS then moved to Altium for designing the PCB.  Because the op-amp is a quad type may as well make it do up to 4 channels.
I added a LM341 adjustable precision reference voltage to improve the reading but rather than have it fixed I made it variable either 2.50V or 4.096V. But after building the board up and played around with it I found that it made the reading worse, well this could be the way I coded it but I tried several methods and picked the best method and never use the LM341
This is all tested and working so I thought I will share it, Itís simple and straight forward to set up and calibrate, Feel free to pass any comments errorís or even post your code if you can get better reading using it or an easier way than mine
Here are some pictures of it working  and the project file that I threw together with sample code for one channel only
« Last Edit: March 26, 2010, 08:01:04 20:01 by Wizpic » Logged

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« Reply #1 on: March 26, 2010, 08:02:12 20:02 »

Here is the book with all the stuff required to build
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« Reply #2 on: March 27, 2010, 12:05:47 12:05 »

Nice one wizpic. I was talking to bbarney about the ADC and voltage measurement. He pointed me out to a nice topic you might want to try out:

http://digital-diy.com/handy-tips/148-adc-calibration.html

This might help you get better results from the existing circuit.
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« Reply #3 on: March 27, 2010, 01:20:33 13:20 »

I shall have a look at that, I only used the sample code just to show, The readings I get are very stable and accurate. Has it is without using V-Ref. But more ways the better

Glad you like it. It's nice to get some feed back

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