Hello, I'm having an issue with this circuit. When I have the load disconnected and read the voltage with the uC, everything checks out fine. The uC gets the same voltage reading as my meter. However, when I start up the pwm (around 90%) to turn on the load (in this case a 12V halogen lamp that draws about 2.9A) then I get a significantly lower voltage reading on the uC than what I see on my meter.
E.g. when load is off my meter reads 12.3V and the uC gets 12.2V. I'm not totally comfortable with that discrepancy but it's close.
When the load is connected (well connected 90% of the time via the uC's pwm) then I get voltage readings of 12.2V on my meter but 11.4V on the uC.
I really don't have an explanation. There is some voltage fluctuation going on at the battery when the MOSFET switches. I've seen this before and I average out the readings on the uC so the voltage spikes should get averaged out. (see the attached scope pic).
I even stored the last 16 ADC register values and saw the low voltage reading consistently. So that rules out the voltage spikes.
I should add that R10 is not installed and just jumpered. Also BATT_V_BOARD is the node between R10 and C3 (connected to the 7805, 5V regulator input)
Any ideas as to why I might be seeing the readings on the uC that don't jive with my meter?
Schematic and scope pic attached.
E.g. when load is off my meter reads 12.3V and the uC gets 12.2V. I'm not totally comfortable with that discrepancy but it's close.
When the load is connected (well connected 90% of the time via the uC's pwm) then I get voltage readings of 12.2V on my meter but 11.4V on the uC.
I really don't have an explanation. There is some voltage fluctuation going on at the battery when the MOSFET switches. I've seen this before and I average out the readings on the uC so the voltage spikes should get averaged out. (see the attached scope pic).
I even stored the last 16 ADC register values and saw the low voltage reading consistently. So that rules out the voltage spikes.
I should add that R10 is not installed and just jumpered. Also BATT_V_BOARD is the node between R10 and C3 (connected to the 7805, 5V regulator input)
Any ideas as to why I might be seeing the readings on the uC that don't jive with my meter?
Schematic and scope pic attached.
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