Easy isn't always easy!

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Easy isn't always easy!

Post by Lenp » Sat Jan 25, 2020 7:37 pm

This not a cry for help but a rant out of pure frustration...!

I need to sort out 4 wires in a group that are all the same color and there are 48 groups to do. Yah, that's 192 wires to identify. There will be connectors soldered onto the ends so the pins must be 1-1, 2-2.... The wire are all gray and are pulled through clear vinyl tubing. I tried markers but some colors just got lost, plus for them being permanent markers, it still rubs off. Nail polish streaked in the tubing, plastic dip was too thick. and colored shrink tube was out of the question due to the time.

Sure, a continuity test with a meter, or buzzer would work but that means I have to change wires on each end for each test. Not good for production. So, I decided to go a 'hi tech' approach; put the connector on one end, any wire order is OK, then put a string of pulses on each connector pin that matched the pin number, 1,2,3,4. Then I could pick the wire at the other end with anything handy, a sounder, earphone, led... to get the wires number and then solder it on...192 times!

Simple eh...
Well I started with an PicAxe 14M2 PicAaxe, sequencing through 4 pins and sending tone bursts that coincided with the pin number.
It worked, but there was too much delay. Since it was all in one loop, the first pin had to wait for all the rest before it sounded again. Not good.
Even interspersing the pins in the loop gave odd delays. The PicAxe M2 parts will do parallel processing...well at least that's what they call it.
What really happens is... if you have 3 'start' programs, line 1 of start1 runs, then line 1 of start2, then line1 of start3, then back to do line 2 of start1 ...and so on. It is just a form of distributed processing! I guess it's good for some uses but for me it was still too long of a delay.

So, like the big boys, I did quad processors! Yes, 4- PicAxe 08M2's each running a loop with a different count. I did the download and testing on a development board but since I didn't want to use 4 boards for this project I decided to board it on a perf board. Simple +V, -V, and output pins, six wires total! After some quick P to P wiring it was a done deal..almost!

It didn't work. It was buggy, noise, bad counts..garbage but most of all unstable. The chip was moved back and forth several times to the development board where it worked as expected, but not in the perf board. Look! It's just power, ground and output. Nothing else! What can go wrong? One chip seemed to work but not all four. Remembering a past puzzle and suspecting noise, I dropped a cap on the power buss, but still no difference! Hours passed, a proper exercise in insanity, and then Eureka!..I forgot something that is often overlooked..FLOATING AND UNUSED PINS.*&%#@*(&@!^% I strapped all those buggers to ground and now it's concert music time with everybody playing their part. Now, as soon as I touch the wire there is the coded pulses with almost no delay since the loops are running independently in each micro , its faster.

At the end, was it the floating pins? The chips did not have problems singly on the development board, and the pins are floating there? It may have been noise coupling from the other micro's chip blanketing the whole board in noise. Well, whatever it was, it's fixed!

Lesson learned. We never really never fully understand what we are doing until after the crisis!

“To invent, you need a good imagination and a big pile of junk.” (T. Edison)
"I must be on the way to success since I already have the junk". (Me)

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