Measurement Circuit Build — Atechnical Man

Here's my approach to building up the monitoring system.

I've got quite a few single sided breadboard PCBs, thanks to a few Radio Shack going out of business sales. I'd rather have double sided with plated through holes, but for this project I think it will be OK. With single sided breadboards, you've got to be careful that components are soldered tight against the board, otherwise the pads will lift off. If mechanical fit isn't good elsewhere, this can lead to shorts and opens down the road.

I decided to use an extra breadboard to align all the pins before soldering. I took a risk that rubber bands would hold long enough to tack things down, and lucked out. It would have helped to show the sandwich being assembled, but you know how it goes. I'll just throw a few pics to show where I got to.

Wrapped sandwich.  Components will be soldered to the top board, bottom board just keeps things aligned until soldering is done.  Six points are tacked so far, those will hold the ADC (more on that later) — Wrapped sandwich. Components will be soldered to the top board, bottom board just keeps things aligned until soldering is done. Six points are tacked so far, those will hold the ADC (more on that later)

Side view of wrapped sandwich.  You can see the ADC boards being held against the header pins and the breadboard.  Nothing is soldered yet on the ADC side of the breadboard yet, that's why I'm going to tack a couple of pins while everythin… — Side view of wrapped sandwich. You can see the ADC boards being held against the header pins and the breadboard. Nothing is soldered yet on the ADC side of the breadboard yet, that's why I'm going to tack a couple of pins while everything is aligned.

Not shown: the next step was to unwrap the sandwich. I forgot that the ADC and level converter boards weren't tacked down, so the all fell onto the garage floor. No problem, the main purpose of the previous steps was to get the headers aligned and tacked to the breadboard. I picked everything up, cleaned, and they all fit easily on the headers again.

Bottom side, all components are tacked at the corners.  Once I've wired up a few of the other pins, I'll remove this solder before adding any wires to these pre-tacked pins.  Otherwise I wouldn't get a good mechanical connection between wi… — Bottom side, all components are tacked at the corners. Once I've wired up a few of the other pins, I'll remove this solder before adding any wires to these pre-tacked pins. Otherwise I wouldn't get a good mechanical connection between wire and pin. Good thing, some of those solder joints are pretty iffy.

After unwrapping and removing the extra board, I soldered all top-side pins. That black 4-pin header is my ground bus, I'll add a power bus too.  I placed a single header pin in the mounting holes of each ADC board, and planned to bend the… — After unwrapping and removing the extra board, I soldered all top-side pins. That black 4-pin header is my ground bus, I'll add a power bus too. I placed a single header pin in the mounting holes of each ADC board, and planned to bend them over and get just a little solder against the big plated hole. The first I tried to bend lifted the pad. For the rest I applied enough heat with the soldering iron to melt the tack below, then leaned the pin and tacked it as shown. I'm happy.

Close-up of the tops.  Unlike the bottom, these are final, so they'd better be good. After this picture, I touched up the middle SCL pin and the right A2 pin, they were light on solder.  The middle SDA looks funny but that's just a re… — Close-up of the tops. Unlike the bottom, these are final, so they'd better be good. After this picture, I touched up the middle SCL pin and the right A2 pin, they were light on solder. The middle SDA looks funny but that's just a reflection. If you see any other problems, let me know. Oh yeah, I'm not allowing comments yet. My loss.

I've hooked up the first ADC, via the level shifters.  Then jumpered in ground, +5V and +3.3V to A0, A1, A2.  A3 is floating. — I've hooked up the first ADC, via the level shifters. Then jumpered in ground, +5V and +3.3V to A0, A1, A2. A3 is floating.

My test code doesn't handle the first measurement of A0 properly, but the rest seem to work pretty good.  A0 is ground, A1 is +5V, and A2 is +3.3V.  All look good.  I've got work to do on the code, and I'll have to play with I2C addre… — My test code doesn't handle the first measurement of A0 properly, but the rest seem to work pretty good. A0 is ground, A1 is +5V, and A2 is +3.3V. All look good. I've got work to do on the code, and I'll have to play with I2C addressing also. For now I'm waiting 10 seconds between trigger and reading the voltage, I'll have to add polling for ready to make it tighter.