well, a relay is good for long periods but not in that case cause the small
size I have to put the circuit.

the 36vdc is so important (this is the main reason why I'm checking it!) so
I am afraid that I have to use some isolation and protection to detect the
missing voltage.

anyway, I will think about what all of you suggest and try to find the best
solution.

Tal

-----Original Message-----
From: pic microcontroller discussion list
[mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Jinx
Sent: Tuesday, December 16, 2003 1:08 AM
To: PICLIST@MITVMA.MIT.EDU
Subject: Re: [EE]: Voltage monitor


> I need help or advice how to monitor the presence of 36vdc and
> get an alarm when it disappear more than 1ms

Simplest would be a PIC - comparator, A/D or plain I/O would do.
Use a 31:5 ratio divider to get safe levels for input. eg 8k2 + 1k2
would produce 4.6V at the junction

A monostable would work as a pulse extender, eg 74123, 4001
etc. Make it with a time period that's long enough to see on a LED
or use its output to disable the input so the output stays latched
after the first pulse. The drop-out could be used to clock a 4017
or drive a latch made from discrete transistors. There are many
ways to do this

If you want information about the drop-out the PIC would be better

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