Can anyone help a newcomer?

[bcd]

The power supply is a regulated DC 6V 300mA plug type. On the board have a 7805 regulator with 10uf + 100nF decoupling capacitors. I have 100nF at the opto encoder supply.

That 6v adaptor won't give a lot of headroom to the 5v reg if it is a standard 7805 style one - this might cause inconsistencies if it is borderline on the regulation and cannot supply the current for the opto LED. I always design at least 2 and ideally over 3v more input than the output of the reg.
Do you have a 9v DC plug pack you could try ?

Bill.

[scopit]

Do you have a 9v DC plug pack you could try ?
Bill.

Hi Bill
The plug pack is switchable, I'll up it to 7.5 & 9v and see if it makes a difference.
I suspect the problem is between the receiver and the PIC as the input to RB0 is clamped at 1.65V.
But at the moment, I'll try anything!
Thanks for the input and I'll get back to you once I've tested
Danny

[scopit]

Here's the latest!

I have upped the PSU voltage and checked all the connections.With a pull up resistor the optical encoder output switches between 1.3 and 4.4 volts.

It will trigger the interrupt the first time it goes high. No further interrupts occur.
If I reset with encoder output low, then the first low low to high transition triggers the interrupt.
If I reset with encoder output high, then the interrupt is not triggered.

If I replace the encoder output with a switch to 5volts, I can trigger multiple interrupts so the software looks like it's working.

Any ideas anyone?
Thanks
Danny

[dhouston]

Look at Table 4.3 and Table 9.2 of the 16F84A datasheet. When configured as an External Interrupt, RB0 has a Schmitt Trigger input buffer which needs 0.8*Vdd for a logic high and 0.2*Vdd for logic low. Your voltages appear to be marginal.

[scopit]

Look at Table 4.3 and Table 9.2 of the 16F84A datasheet. When configured as an External Interrupt, RB0 has a Schmitt Trigger input buffer which needs 0.8*Vdd for a logic high and 0.2*Vdd for logic low. Your voltages appear to be marginal.

Thanks Dave, I'll check the voltages again but from your post, the problem may be on the logic low.

[dhouston]

Thanks Dave, I'll check the voltages again but from your post, the problem may be on the logic low.

I agree - after sensing the first high, it never senses a low, so it cannot sense another low-to-high transition.

[dhouston]

Thanks Dave, I'll check the voltages again but from your post, the problem may be on the logic low.

It appears that after sensing the first high, it never senses a low, so it cannot sense another low-to-high transition.

[scopit]

It appears that after sensing the first high, it never senses a low, so it cannot sense another low-to-high transition.

Thanks Dave you were right. I removed the pull up and in the process found a dry joint. This may have been the source of the issue in the first place, but was causing the intermittent behaviour.

Interrupt is working now and I can continue working through the testing.

Thanks everyone for your help.
Danny