SPYDAR Circuit Monitor

Intermittent failures in electronic systems are some of most difficult to diagnose.  This device is designed to run for days at a time looking for a failure and logging the event.
The unit is based on a PIC16F84.  Six digital data lines are brought in via a 74hc165 shift regiser.  The shift register is connected to a set of series resistors so that any voltage from about 3 volts to about 30 volts will read as a high condition.  A single analog line is read using an ADC8031.  (Note: with todays PICs, it would be better to use one with the A/D built in).

Once activated, the unit counts off time down to 1/100 second.  Any change of state of the 6 digital lines causes it to store the time, the state of the six lines and one analog voltage.  If nothing happens within 10 minutes, it logs it as a non-event.   The reason for this is to allow more dense storage of times in the eeprom by storing delta times between events.

The DOS based program that reads out the data constructs an elapled time table based on summing delta times.   This is writen to a text file - see this sample.

The circuit is designed to shut itself off either manually or when the eeprom is full.  No power is drawn in the off mode.  The DOS capture program is written for COM1 and connects to a stereo mini jack on the unit.

Operation:  Connect a 9 volt battery to the unit.

(without connection to computer serial port)

Switch on RB7 plays a medium tone burst and starts the unit running.

Switch on  RB6 plays a higher tone burst and turns the unit off.

(with computer com port connected)

Switch on RB7 plays just 4 tones and enters communication mode.   Run PC software to download datat to text file.

Switch on RB6 plays 2 tones and powers off.

So far this unit has facilitated the repair of one RV-based propane refrigerator.

Provided for you use:  Schematic, device Source file, device Object file, DOS C Source file,  DOS