HI
I have a board built up. I forgot to have a ground plane put on it. I know I screwed up there so no need to take me to task on that one.
I am testing this board with a racing ignition operating on my test bench. In essence what this deal does it controls a digital pot (AD 5220 50k) based on the position of the BCDs. For example when SW2 is at 5, the digital pot moves to 10k. The Wiper and one leg of the digital pot go to the ignition system. I am measuring the resistance between the wiper and leg with a Fluke Meter.
When one of the pins on Conn3 get 12v, it grounds out a pin on the pic and the code instructs the digital pot to step to 0 ohm.
So I have a 12v battery on my test bench with a MSD ignition, coil, spark plug off the coil and a motor turning a crank trigger wheel. I hold the trigger pickup to the crank trigger wheel and the signal triggers the ignition to fire the plug.
My digital pot device is using the same power and ground, just like in a race car. The housing is grounded that holds the board.
When I watch the ohms between the wiper and leg while the ignition is firing the ohms go from 6k to 60k then back to 0ohm and then climbs to up again.
This leads me to think the PIC itself is fine but the two inputs to the digital pot (CLK and U/D) are having some problems. I also have a couple LEDS that go high when an input from CONN3 is highand they do not do anything stupid. I do have the U/D pin pulled high with a 10k resistor and the pot is always incrementing high even after starting back at zero.
What can I do to help the CLK pin? I am not too sure if a pull-down or cap or both would be the best. Or maybe something else.
I am attaching the schematic and board drawing.
Thanks in advance.
Toby
I have a board built up. I forgot to have a ground plane put on it. I know I screwed up there so no need to take me to task on that one.
I am testing this board with a racing ignition operating on my test bench. In essence what this deal does it controls a digital pot (AD 5220 50k) based on the position of the BCDs. For example when SW2 is at 5, the digital pot moves to 10k. The Wiper and one leg of the digital pot go to the ignition system. I am measuring the resistance between the wiper and leg with a Fluke Meter.
When one of the pins on Conn3 get 12v, it grounds out a pin on the pic and the code instructs the digital pot to step to 0 ohm.
So I have a 12v battery on my test bench with a MSD ignition, coil, spark plug off the coil and a motor turning a crank trigger wheel. I hold the trigger pickup to the crank trigger wheel and the signal triggers the ignition to fire the plug.
My digital pot device is using the same power and ground, just like in a race car. The housing is grounded that holds the board.
When I watch the ohms between the wiper and leg while the ignition is firing the ohms go from 6k to 60k then back to 0ohm and then climbs to up again.
This leads me to think the PIC itself is fine but the two inputs to the digital pot (CLK and U/D) are having some problems. I also have a couple LEDS that go high when an input from CONN3 is highand they do not do anything stupid. I do have the U/D pin pulled high with a 10k resistor and the pot is always incrementing high even after starting back at zero.
What can I do to help the CLK pin? I am not too sure if a pull-down or cap or both would be the best. Or maybe something else.
I am attaching the schematic and board drawing.
Thanks in advance.
Toby
Attachments
-
66.7 KB Views: 16
-
53.6 KB Views: 16
Last edited by a moderator: