I just discovered new way to kill a Teensy. However they are so tough, the damage was only partial. So I have a question or two about the likely damage and whether I should even consider keeping the damaged Teensy for an emergency backup.
I have a Teensy 3.2 running my gin still. It measures temperatures flow rate, liquid level etc and controls the heater and cooling pump valves and fan. All works very well. I have a simple 4 line LCD (I2C) a bunch of one wire temp sensors and am using a touch input as a liquid level sensor.
I was doing a little improvement to the still and forgot to turn off the 220 volt supply to the heater SSR. I dropped a grounded guy cable and guess where it landed? Right on the (now protected) 220 volt line. Sparked and melted the cable. The still continued to operate and run the heater. This requires that all sensor inputs are valid. The problem is that the display regularly becomes a bunch of gibberish. I have code that refreshes the LCD whenever you change display screens. The code that is running in one mode never messes up the display but others do. Does it sound like the I2C lines were damaged or the flash memory itself?
I am not interested in figuring out what code causes the display to go bad. The solution was to replace the Teensy and it all is working as it did just before the accident. My questions are:
even though the ground was well connected to the utility ground, i am sure i got one hell of a spike on it. The teensy ground is not connected to the metal of the still nor to the utility ground. My guess is that the surge went through the touch input that is connected to ground via the boiler fill. So, is this bad way to sense liquid level? Otherwise I would need to make a bridge / comparitor circuit and isolate it optically. I know that is the right way but are there simpler options? Is there some sort of simple protection device I can use for the touch input such as a large resistor and maybe a MOV?
I have a Teensy 3.2 running my gin still. It measures temperatures flow rate, liquid level etc and controls the heater and cooling pump valves and fan. All works very well. I have a simple 4 line LCD (I2C) a bunch of one wire temp sensors and am using a touch input as a liquid level sensor.
I was doing a little improvement to the still and forgot to turn off the 220 volt supply to the heater SSR. I dropped a grounded guy cable and guess where it landed? Right on the (now protected) 220 volt line. Sparked and melted the cable. The still continued to operate and run the heater. This requires that all sensor inputs are valid. The problem is that the display regularly becomes a bunch of gibberish. I have code that refreshes the LCD whenever you change display screens. The code that is running in one mode never messes up the display but others do. Does it sound like the I2C lines were damaged or the flash memory itself?
I am not interested in figuring out what code causes the display to go bad. The solution was to replace the Teensy and it all is working as it did just before the accident. My questions are:
even though the ground was well connected to the utility ground, i am sure i got one hell of a spike on it. The teensy ground is not connected to the metal of the still nor to the utility ground. My guess is that the surge went through the touch input that is connected to ground via the boiler fill. So, is this bad way to sense liquid level? Otherwise I would need to make a bridge / comparitor circuit and isolate it optically. I know that is the right way but are there simpler options? Is there some sort of simple protection device I can use for the touch input such as a large resistor and maybe a MOV?