I know what I need (at least I think I do) but I don’t know exactly what I need.
I have a device that outputs 1v AC. When it is switched on, I want it to in turn switch on another device that outputs 12-16v DC.
I believe I need to connect a transistor to the 1v AC output and then said transistor to a relay which is connected to the 12-16v DC output device.
Trouble is, I can’t figure out the exact specs of the transistor and relay that I need. (And it’s not like the manufacturer’s descriptions are much help.)
Can anybody help out with this and tell me exactly what I need?
That seems rather odd for an output - what sort of device is outputting 1V AC? The probem is, if you feed AC into a transistor fast enough to handle the frequency, the output then switches on and off at the AC frequency. This could get complicated pretty quickly, as having only 1V to work with means in rectifying it into a DC signal to operate a transistor will use up most of that. I’m thinking this might need multiple transistor stages, a sensitive one to work on the less than 1/2 volt that would be left over after rectifying the 1V signal, and then a second one with enough power on the output side to trigger a relay.
I’m with Randy on this one. What is the source of the 1VAC? I was in electronics for over 50 years and can’t remember seeing a 1 VAC power supply. You will need to convert the AC to DC if you are going to use a transistor to drive a relay if that is your only route.
Mel
Modeling the early to mid 1950s SP in HO scale since 1951
It’s a Walthers Traffic Ligjht Controller. When the Controller illuminates the red LED, I want it to also activate a relay that will feed power to am electromagnet.
Not reluctant. That would be weird. This forum is causing a delay in my posts appearing. No, I haven’t put a multimeter to the Controller, just going by the manufacturer’s documentation right now.
since the input (1V AC) is at least greater than the voltage drop across the base-emitter junctions, maybe a small resistor is needed to limit the current. I’m not sure that the reverse voltage needs to be worried about, but if it is, a reversed bias diode across the B-E should work.
yes the transistor would only conduct < half each cycle. But that might be enough to drive another transistor to control a charge on a capacitor (perhaps discharge it) which drives yet another transitor to hold the relay as long as the AC signal is present.
Well, if it’s lighting a red LED, then I’m pretty sure it’s more than 1 volt (I don’t know of any LEDs that will light at 1 volt). I would replace the LED with an optical isolator, then it would be pretty easy to control whatever you want from that.
I agree with CSX Robert, You should be able to parallel the red LED with a optical isolator and direct drive a small relay. I have several doing exactly that, 4N35 work great.
Mel
Modeling the early to mid 1950s SP in HO scale since 1951
It will show as 1V because the lines to the LEDs are at minimum muliplexed and likely Charlieplexed to save IO pins. It’s definitely putting out more than 1V, but it is just a short pulse, persistence of vision takes over after that, each of the LEDs is really only blinked on for a short while. For the extreme example, see the Digitrax SE8C. From 10 wires they drive 4 signal heads of 3 LEDs each (12 LEDs), and while their example shows them being used in a typical control point where you would never have signals facing opposite directions both be green, each head IS independently controlled, because you don’t have to use them only as shown in the example, you can take the 4 heads from one output and line then up as intermediate signals if you want. A Charlieplexed LED output would appear to change polarity relative to the circuit common, part of how it works is by taking advantage of the fact that LEDs are still at heard diodes and only conduct in one direction.
Such lines really aren’t meant or suitable to drive something other than an LED. And usually only 1 LED at that, with a higher load the peak brightness will be less adn the fact that the LED is really flashing on and off may become noticable. However, an optical sensor is probably the best option - an optoisolator is really just an LED and phototransistor in a single package, that would get you close to the same ‘AC’ but at a higher voltage which woudl then allow for smoothing and filtering.
previous comments as to the 1v … if it’s really a led [and not an incandescnt] , the applied voltage should be 2v or better for colored leds, and would more than likely be dc , opto couplers would work well to drive a relay, unless the current is low enough to be fed through the opto directly 4n35 is around 100ma , doubtful the electromagnet would be that low …
