I made a simple counter with a pic16F84. The circuit is:

        RB4             : first counter input
        RB5             : second counter input
        RB0,1,2,3,6,7   : not connected
        RA0,1,2,3       : not connected
        RA3             : pull-up resistor to Vcc (10K)
        Osc1,Osc2       : 4 Mhz resonator
        MCLR#           : Reset circuit with 100nF, 10K and 1N4148
                          (as Microchip datasheet) plus a serial 1N4148 for
                          in-circuit serial programming.

The input counter are normally high (5V) and drive from external circuit.
RA3 is used for serial print but normally not connected during normal
operation (the printer is connected only during printing). All pin are
programmed as input pin (RA3 as output when print).

The circuit is mount inside a machine that provide power (is used a
switching feed) and counter signal (the main board is a microprocessing
board).
All circuit are mounted in a box with a keyboard and monitor.

The machine must pass a test with a high voltage discharge on the front
panel. The discharge is generated with a electrical ignite gas (normally
used to light a ring).

The circuit seems to work fine but at the first discharge the pic is reset
(not a really problem) and after some seconds it become hot (it seems to be
a short circuit somewhere but where???) and after 20 seconds it break.
To avoid Pic break I must turn off the machine quickly.

Where is the error? Someone have a idea?

TIA

Giorgio.


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Alboni Giorgio
Faenza (Ra) ITALY
E-Mail: rac1337@racine.ravenna.it ICQ# 24774821

http://www.geocities.com/SiliconValley/Heights/5444
(Last Update: 15/03/1998)
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