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MULTI-CHANNEL PROGRAMMABLE TIMER

by Noel Rios

Start ý Circuit Description ý Checking and Troubleshooting ý Setting Up the Device ý Sources and PDF

CHECKING AND TROUBLESHOOTING

In checking digital and microcontroller circuits, the following are important when using a voltmeter and logic probe.

ý POWER is present

ý CLOCK is present

ý activity in the data bus

ý activity in the address bus (check transparent latch U2)

ý program data is read /OE and /CS of EPROM pins are active

ý data is read and written /RD and /WR are active

Do not wire the solid-state relay until you check the connections between the pins of all the ICs, using a multitester or continuity tester. So it will be easy to troubleshoot later, donýt mount the circuit board to a suitable enclosure, until you first check the circuit. Do not plug in the ICs, until after you check the power.

After wiring the power supply section, check the DC supply at the supply pins of the ICs. Pins 40, 28, 24, 16, and 14 should read 5 V. Pins 20, 14, 12, 8, and 7 should be at ground potential. Itýs not enough for them to be at zero potential, they must also be connected to ground.

After Power is OK. Turn off the device and plug in the 80C31 microcontroller. Pin 18 should be active or pulsing. This means clock is present. Turn off the project and plug in the EPROM. After powering up, youýll see activity or pulsing in the data bus and address bus. It is fetching program memory by checking the /OE and /CS of the EPROM.

Also, check the LCD display, it should read "PC Timer V1.0". If all seems fine, plug in the remaining ICs one at a time after powering off and see which part, when inserted, causes it to malfunction. If the project ceases to display the message in the LCD, the most probable cause is a wrong connection in that IC.

In accessing the DS1287 and 8-bit input port for the keypad, pins 15 and 14 of the 74HC138 (U5) should be pulsing. If theyýre not, check if pins 1, 2, and 3 are pulsing. Also, to decode the memory locations properly, the address lines connected to the 74HC138 (U5) should be correct.

If the keypad cannot be accessed, try checking if the /RD (pin 10 of U1) is connected to pin 2 of 74HC32 (U7). Also, check if pins 1 and 19 of U6 are pulsing.

If the circuit board is functioning properly, place it in a suitable enclosure. The enclosure should provide holes for the switches, LCD, fuse holder, convenience outlet, and the power plug. And finally, wire the solid state relay, fuse, and convenient outlet. Check the connections and check for shorts or faults.

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