100uF bypass Caps?

[For The Popcorn]

I am having a heck of a time getting I2C working with MCP23017 port expander. I've checked the connections, verified the values of my pullup resistors (4.7k) and so on but code that has worked before isn't working for me on these new boards.

While looking at the board, I noticed my 0805 100nF bypass caps seem unusually thick – they're about as thick as they are wide. I don't have a capacitance meter, but my "component tester" says they are around 130uF, not 100nF. It's possible that my assembler screwed these up.

It doesn't seem like this should matter much, but there are about 10 of them on the board. Do you think this would make a difference? Yes, reaching for straws at the moment....

The caps to the right of the crystal are 22pF, and I expect 100nF (C53 & C2) should be about the same thickness.

 

[ChrisP58]

The things I do for science....View attachment 149958

Is the sensor food safe?

 

[For The Popcorn]

Is the sensor food safe?

Well, no ill effects yet

 

[schmitt trigger]

Try Diet Coke. It’s corrosiveness is equivalent to concentrated hot hydrogen peroxide. T-Stoff.

 

[For The Popcorn]

Try Diet Coke. It’s corrosiveness is equivalent to concentrated hot hydrogen peroxide. T-Stoff.

It was Diet Code. Still not dead yet

I went through the effort of entering a thermistor resistance table into Excel (from a photo which is pretty slick), calculating the ADC output for the 10k/thermistor voltage divider, plotting the curve and concluding over the temperature range I'm concerned with, it's close enough to a straight line.

Then I calculated the resistance of the thermistor from my ice Coke bath (gently agitating to reach the lowest value) and set to work trying to figure out the equation of the line. Ugh. Time for a shower.

The light bulb turned on. I don't really care what the resistance is, because I know the ADC/temperature relationship is. And I have a point at 0°C. The spec for the temperature sensor is 10k @ 25°C. The voltage divider will be reading half its max value with the 10k/10k voltage divider. Two points.

Everyone knows the equation of a line:

y = mx + b

Where

m = slope = rise/run

b = y intercept

The slope was easy, but calculating the intercept is lost in the reaches of time.

AI to the rescue:

"Equation of line (x1, y1), (x2, y2)"

Seconds later, results with "show your work." Maybe there is something to AI.

 

[For The Popcorn]

Making good progress on this now. The port expanders are doing their thing reading switches and controlling ports and the ADC reading thermistors and a current sensor.

I did have an oh-crap moment today. I forgot to connect the output of the home sensor to the micro – it's not coming through the port expander as I want to monitor it without delay. This vending machine supplies 24 volts through its switches, connected to voltage dividers to provide a 5 volt signal to the port expanders or micro. I connected its bodge wire from its voltage divider to an unused port pin connected to the 6th pin of the ICSP connector. It was an easy place to make a connection.

Testing this input today I connected a jumper between +24v and.... not the pin the switch connects to but the easy-to-find port pin on the ICSP connector. Crap. I realized my error almost immediately. The code stopped running. Reset did nothing. The micro was very hot, even after the jumper was removed. Dang it. At least the DIP micro was in a socket and nothing else on the board was damaged!

 

[ChrisP58]

Been there, done that. Worn out the t-shirt.

 

[For The Popcorn]

I'm just glad it didn't take out any of the smt chips.

Way back in the old days, I was adding remote control to a 1" instrumentation tape:recorder. Somehow I managed to blow out every chip in the divide by billions chain that went from the capstone encoder to footage counter display. At least they were through-hole DIPs.