piclist 2001\09\08\130634a >
Thread: Homebrew ICD problem fixed
www.piclist.com/techref/microchip/devprogs.htm?key=icd
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face BY : Michael Maiorana email (remove spam text)



Just an FYI for anyone who wants to build the "build your own ICD". Mine
failed self test with "incorrect MCLR voltage, check pin 1".  Checks with a
volt meter showed the Vdd and Vpp voltages as correct (5 volts and 13
volts). From the MPLAB options screen, the voltages read way too high, 6.8
volts and 21 volts. The ICD uses an LED as a voltage reference. Apparently,
they use a specific LED that has a 2 volt drop across it. My LED only
dropped 1.4 volts. With the reference voltage too low, the ICD read the
voltages as too high. This seems like a strange design to me...

I put a 47 ohm resistor between the cathode of the LED and ground which
raised the reference voltage to 2 volts. Now, the voltages read correctly
and the unit passes self test. Just for reference, the unit also will
program and debug correctly as well.

Regards,
Mike M.

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