arhi
Member
I have machine working in dry environment and as there's bunch of moving parts there is a build up of static electricity. I managed to insulate electronics pretty good from all external "interference" but I still have one nasty line coming in. The problem is in a NTC resistor that is sitting embedded in aluminium heater block that can collect some static from time to time. The worst problem is current design that goes like
so if the spark from the Al block hit the thermistor leg that is connected directly to ADC input of PIC32MX (that is not even 5V tolerant) I get all kind of weird issues (PC jumps to unknown location, PIC reset, PIC freeze). The WD makes sure no real damage can happen when this happens (except if once I get spark powerful enough to burn the PIC) but I want to solve this as fast and as simple as I can. I have 3 of these circuits going to 3 different ADC inputs.
As the PCB is already laid in and not cheap to change, mine idea was to add, inside the connector something like this:
Now, questions .. the Rx shoud be 0 in order to have the same voltage on the ADC as there was before this change (but I was never very good with op-amps) anyhow, does anyone have idea if this is viable solution at all - it's not that I can test easily if spark will travel trough op-amp or not .. I also considered adding a 3V zener between +op-amp and GND
So - Any suggestions? Better calculation for Rx and Ry? (I know I suck with op-amps, the little I know I learned on this forum from nice guy's like audioguru, ericgibbs and others ) .. better way to filter the input and prevent nasties to kill my pic? all the digital lines go trough opto-couplers but I can't solve this 3 analog ones
Code:
3V3
|
600R
|
+-----ADC INPUT ON PIC32MX
|
NTC 200K
|
GND
so if the spark from the Al block hit the thermistor leg that is connected directly to ADC input of PIC32MX (that is not even 5V tolerant) I get all kind of weird issues (PC jumps to unknown location, PIC reset, PIC freeze). The WD makes sure no real damage can happen when this happens (except if once I get spark powerful enough to burn the PIC) but I want to solve this as fast and as simple as I can. I have 3 of these circuits going to 3 different ADC inputs.
As the PCB is already laid in and not cheap to change, mine idea was to add, inside the connector something like this:
Code:
3V3
|
600R
|
+----------[ferite bead]---[ + MCP6021 out]--+ ADC INPUT ON PIC32MX
| [ ] |
| +---[ - ] |
NTC 200K | |
| +---------Rx-----------+
GND |
10K (Ry)
|
GND
Now, questions .. the Rx shoud be 0 in order to have the same voltage on the ADC as there was before this change (but I was never very good with op-amps) anyhow, does anyone have idea if this is viable solution at all - it's not that I can test easily if spark will travel trough op-amp or not .. I also considered adding a 3V zener between +op-amp and GND
So - Any suggestions? Better calculation for Rx and Ry? (I know I suck with op-amps, the little I know I learned on this forum from nice guy's like audioguru, ericgibbs and others ) .. better way to filter the input and prevent nasties to kill my pic? all the digital lines go trough opto-couplers but I can't solve this 3 analog ones
Last edited: