driving small relays with LM3914?
OK, I hear what you are saying. I have since talked some more to my partner about the issues and he suggests that we should have the facility to record for a week or two! That makes sound recordings way too big!
I've gone back to my original idea of recording voltages via LM3914 and relays - using a security system....
What kind of voltage and current can the LM3914 "supply" to drive small relays? or do I need to give that task to a switching transistor for each output?
Any ideas where I can find a circuit to do this?
Someone asked for application information: I work part-time in the security system industry helping a mate troubleshoot systems. We come across a few systems where there are 6 IR motion detectors wired in series (all of them normally closed). When things go wrong, they alarm (open their relays) lots of times at random times and for random periods.
The security guard goes there and finds absolutely nothing - all the while the alarms keep going (or start again later or the next night).
Of course because of the way they were wired, we can't tell which one is doing it!
These things are expensive and we can't just replace them all without good reason, and often there are environmental reasons for it - eg warm air circulating in weird patterns, even mice having a party on a curtain rod near a sensor or whatever - so that replacing them does not solve the issue!
Our solution is of course to rewire the building when it can be justified at all, but mostly these are schools with low budgets who can't afford that.
To track where the hits come form, I want to put a resistor across the alarm terminals of each sensor - a different value for each sensor. That way I could simply measure the voltage drop when one sensor opens and identify it by its "voltage drop signature".
It is relatively cheap (here, if you know the right people) to have an alarm panel monitored without getting any guard responses. So we now want to set up a testing panel/dialler with six inputs - provided by the relays pulled by the LM3914 in response to six different voltages. The friendly security firm then e-mails us a log every night or week or whatever and we will know which sensor went into repeated alarms (called 'continous single hits' or 'multiple alarms' in the industry). We can then either replace the sensor that plays up or relocate it away from a heat source or move the mouse dance floor away from the sensor.
The system would be powered on along with the existing system, which also passes on the alarms on the "whole circuit" for responses as usual.
I hope that helps a little in understanding the issues. Sorry it is so lengthy....
All we need now is a circuit to drive 6 relays in response to six voltages
Cheers,