I used to experiment with electronics years ago. I was never advanced but I can usually find my way around basic circuits. I had an idea for a very simple circuit, but something is happening that I just can't figure out.
The circuit:
The circuit layout is in the attachment. The relay is a DPDT latching relay (this series). In the "reset" position, pins 9 & 10 and 4 & 3 are connected. In the "set" position, pins 9 & 8 and 4 & 5 are connected.
I am using it by applying +12V to pin 12 to reset it and +12V to pin 7 to set it.
What it is supposed to do:
When power flows into pin 12, the relay is reset and the same power source is connected to the blue output line through pin 10. This way, when power is removed, the output goes dead, even through the relay is still in the reset position. But if power is removed from pin 12 and then applied to pin 7 via the momentary switch, the relay closes in the set position, applying a constant 12V to the blue output through pin 5, so that the line remains active even though the switch is open. When power is once again applied to pin 12, the relay resets.
The application is on a motorcycle. There are times when it is useful to have auxiliary power for some items (e.g. charge camera batteries) without running the headlight and other needless items. So pin 12 is connected to a power source that comes on when the key is turned. Pin 7 is connected to a switch. When I want auxiliary power, I turn the key off and press the switch. When the key is next turned on, the relay is reset (thus saving me from draining the battery by forgetting to turn off a mechanical switch).
What it is doing:
The blue line is meant to go to an automotive relay controlling an auxiliary fuse panel. When it is connected to a digital panel meter, it works exactly as expected. But as soon as it is connected to the automotive relay, it will generally not reset when power is applied to pin 12. I say "generally" because sometimes it will (about 10% of the time, let's say), making me think that something is forcing the coil back to the set position, and that once in a while my connecting and disconnecting of the power catches the relay in the proper position.
If I disconnect the link between pins 5 and 10 (where they tie together to activate the automotive relay), the circuit works. If I connect a diode between pin 10 and the relay line, with the cathode at pin 10, the circuit resets properly, but of course I cannot power the relay through pin 10, because the diode is blocking the flow.
All this is completely counter-intuitive to what I would expect. There should be no interaction between the two coils, and the one point where there is a potential for interaction (the connection between pins 9 and 12 - which should be disconnected in the set position) would force the relay into the reset position, not the set position, which seems to be what is happening.
I've rewired the circuit twice and it's now on a breadboard, so I am sure that it isn't a short or other wiring error. The same thing happens both on the bike and from a 12V power supply on my desk.
I've gone over this in my head again and again, and I'm sure I'm missing something really, really obvious. Can anyone help?
The circuit:
The circuit layout is in the attachment. The relay is a DPDT latching relay (this series). In the "reset" position, pins 9 & 10 and 4 & 3 are connected. In the "set" position, pins 9 & 8 and 4 & 5 are connected.
I am using it by applying +12V to pin 12 to reset it and +12V to pin 7 to set it.
What it is supposed to do:
When power flows into pin 12, the relay is reset and the same power source is connected to the blue output line through pin 10. This way, when power is removed, the output goes dead, even through the relay is still in the reset position. But if power is removed from pin 12 and then applied to pin 7 via the momentary switch, the relay closes in the set position, applying a constant 12V to the blue output through pin 5, so that the line remains active even though the switch is open. When power is once again applied to pin 12, the relay resets.
The application is on a motorcycle. There are times when it is useful to have auxiliary power for some items (e.g. charge camera batteries) without running the headlight and other needless items. So pin 12 is connected to a power source that comes on when the key is turned. Pin 7 is connected to a switch. When I want auxiliary power, I turn the key off and press the switch. When the key is next turned on, the relay is reset (thus saving me from draining the battery by forgetting to turn off a mechanical switch).
What it is doing:
The blue line is meant to go to an automotive relay controlling an auxiliary fuse panel. When it is connected to a digital panel meter, it works exactly as expected. But as soon as it is connected to the automotive relay, it will generally not reset when power is applied to pin 12. I say "generally" because sometimes it will (about 10% of the time, let's say), making me think that something is forcing the coil back to the set position, and that once in a while my connecting and disconnecting of the power catches the relay in the proper position.
If I disconnect the link between pins 5 and 10 (where they tie together to activate the automotive relay), the circuit works. If I connect a diode between pin 10 and the relay line, with the cathode at pin 10, the circuit resets properly, but of course I cannot power the relay through pin 10, because the diode is blocking the flow.
All this is completely counter-intuitive to what I would expect. There should be no interaction between the two coils, and the one point where there is a potential for interaction (the connection between pins 9 and 12 - which should be disconnected in the set position) would force the relay into the reset position, not the set position, which seems to be what is happening.
I've rewired the circuit twice and it's now on a breadboard, so I am sure that it isn't a short or other wiring error. The same thing happens both on the bike and from a 12V power supply on my desk.
I've gone over this in my head again and again, and I'm sure I'm missing something really, really obvious. Can anyone help?