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So just remove the diode. You may be getting a false reading on the cathode. What is the output on the opto?
SG
LP0701 P channel FET drive problem from ICM7242 timer
- Thread starter elandri
- Start date
SG
Without the diode it resets the opto led when the circuit is powered from the PSU. Doesn't work when power is derived via opto.
Another aspect of this circuit (which we haven' go as far as yet!) is that it needs to hold power up for a second or two after Reset so that the radio transmitter it's attached to can transmit a message relaying that change of status.
I'd thought of using a 2nd 7242, triggered by the output of the first with both outputs feeding a NAND Gate so that either or both of them being low would give a positive output to power the opto.
Feasible?
I'd thought of using a 2nd 7242, triggered by the output of the first with both outputs feeding a NAND Gate so that either or both of them being low would give a positive output to power the opto.
Feasible?
Hoping that the additional layer of logic between timers and opto will get around the problems we're having.
Would have been nice if the diode had worked as could have just held the opto up with a C.
Don't have any cmos NAND gates so will be a few days before I can try this.
Really appreciate your help. Thanks!
Would have been nice if the diode had worked as could have just held the opto up with a C.
Don't have any cmos NAND gates so will be a few days before I can try this.
Really appreciate your help. Thanks!
No problem. I'll work on some other solutions in the meantime.
SG
We have lift-off!
Didn't work at first. D1 in your pic prevented the voltage on pin 2/6 of the 555 from getting above about 1.9V so it didn't trigger. Works fine without it. Doesn't matter if the radio Tx input is reset by the the reset switch or the 7242.
Also, with D3 and the 1K in the circuit from the 555 through the opto LED the LED wouldn't hold on. With the R removed it's still only passing 2.4mA. The 4.7K in series with supply lets 2.9mA through when Set is pressed.
I put a 2.2M in for R1 to ensure the Reset transmission is completed before power off and you can see the Tx led come on and go off, say 1001 and then see the 3.3V disappear.
All very satisfying.
I've tried measuring current when circuit is idle and I can't even see a uA.
I've been testing with a 100K in place of the 2.2M 7242 timing R so I don't have to wait 5 mins for timeout so I'll go and check that out but I think we are there.
So, circuit now looks like this:
Are you accepting proposals of marriage
?
Seriously, I'd been banging my head against this for a week and beginning to despair of ever seeing it working so I am really grateful for your assistance.
Regards.
John
Didn't work at first. D1 in your pic prevented the voltage on pin 2/6 of the 555 from getting above about 1.9V so it didn't trigger. Works fine without it. Doesn't matter if the radio Tx input is reset by the the reset switch or the 7242.
Also, with D3 and the 1K in the circuit from the 555 through the opto LED the LED wouldn't hold on. With the R removed it's still only passing 2.4mA. The 4.7K in series with supply lets 2.9mA through when Set is pressed.
I put a 2.2M in for R1 to ensure the Reset transmission is completed before power off and you can see the Tx led come on and go off, say 1001 and then see the 3.3V disappear.
All very satisfying.
I've tried measuring current when circuit is idle and I can't even see a uA.
I've been testing with a 100K in place of the 2.2M 7242 timing R so I don't have to wait 5 mins for timeout so I'll go and check that out but I think we are there.
So, circuit now looks like this:
Are you accepting proposals of marriage
?Seriously, I'd been banging my head against this for a week and beginning to despair of ever seeing it working so I am really grateful for your assistance.
Regards.
John
Your welcome. Glad it's working but a couple of things seem array. Removing D1 is OK but I think you should put a 1K resistor between pin 5 and the RESET switch. The way it is now when you press the switch you are putting the supply voltage directly to pin 6 of IC1 which is low so effectively a short although brief.
This issue with D3 makes no sense unless the output from the 555 is too low. The 555 output should be almost supply voltage when high. Replace D2 on your schematic with a 1K resistor and read the output.
SG
LMC555CN to be precise which I think is OK?Well theeeeeeeeeeere's your problem.
SG
Probably OK but that's why you were having the issues with D1 and D3. I just tried the LM555 in my setup and the output on pin 3 is only 2 volts. That explains the drop out with R3.
SG
Could you clarify which pin you want to 1K on pls? Reset puts supply onto pin 5 but that's an input pin that's design to be pulled up and down?
Should it go between 5 and 6 so that pin 6 isn't pulled up too hard?
