# Relay query

Discussion in 'General Electronics Discussion' started by HornDog, Nov 28, 2013.

1. ### HornDog

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0
Nov 28, 2013
Hi guys and gals, a have a basic electronics knowledge but nothing special so bear with me!

I have a solenoid that triggers on a 5v input. However the 'trigger' for this is a voltage that is off at 0.17v and on at 0.3v

I assume I need a form of relay in the middle that will take the trigger voltage, a steady 5v and then output the 5v to the solenoid when the trigger goes from low (0.17v) to high (0.3v)

The triggers are low voltages as they come from a radio receiver, is there some kind of programmable relay that can be set to what voltage to trigger on?

Or do I need to increase my trigger voltage? if so how?

Or is my knowledge so poor that this is completely the wrong approach!

Dave

Last edited by a moderator: Nov 29, 2013
2. ### CDRIVEHauling 10' pipe on a Trek Shift3

4,960
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May 8, 2012
Firstly: Low = 170mV, High = 300mV is a recipe for erratic operation. That's an awful noise window. There is no logic family on this earth that operates with a window that narrow. Please explain where you're picking off this signal on the receiver.

Secondly: We can give you what you need but you must understand that there's more involved here than voltage. The solenoid has current requirements which are typically substantial. You can't drive it directly from the receiver unless the receiver was designed with a control output. If so, they usually have a set of dry contacts to use as a switch. Doubtful your receiver has this though.

Chris

3. ### HornDog

2
0
Nov 28, 2013
Thanks

Thanks for the response,

The receiver has multiple outputs as you would expect for each channel of radio used. One 'aux2' I have programmed with the controller to activate on a certain switch. The output from the receiver has three pins, ground, steady +5v and what I can only think is the trigger. Taking a voltage from the trigger and ground gives me those low mV readings.

Your message did get me thinking though, as the receiver has no external power to it. but has five other outputs as described above plugging into the main controller on the board. So in my simple thoughts it must be drawing power from the controller on the gnd and +5v and could it be likely as my volt meter is not grounded correctly thus the odd switching results?

Either way I have found a better solution now! I have purchased a ready made switch that runs off the receiver that will switch 5v from another source - designed exactly for what I need. Not arrived yet but at a tenner worth the risk!

Thanks for your thoughts - Id be interested if you think any of my ramblings above are even remotely correct.

Dave

4. ### CDRIVEHauling 10' pipe on a Trek Shift3

4,960
651
May 8, 2012
That's difficult to answer. You alone know what you have there and you alone know what you ordered and are waiting for. The advice we post is based on the information the OP's give us. Currently, we have no schematics, photos, links, model numbers or any of the pertinent data necessary to give you intelligent advice. Heck, the term "Radio Receiver" is very broad.

However, since I love a challenge I'm going to take a wild guess at how your output ports are structured. My guess is the pin you're measuring from ground is configured as an....

Open Collector Output

or

Open Drain Output

or

a set of Dry Relay Contacts.

You can test this by placing your DMM in the Continuity (DIODE) mode. Connect the neg probe to ground and the pos probe to the control pin. Be very careful to not accidently touch the 5V pin!

An alternative test can be done with a 1K resistor in series with the Anode of an LED. Connect the other end of the resistor to the +5V pin and the LED 's Cathode to the control pin. When the control pin goes low, which I believe it does, the LED will light.

Chris

Last edited: Dec 1, 2013
5. ### KrisBlueNZSadly passed away in 2015

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Nov 28, 2011
I was thinking the same thing Chris. Good advice.

6. ### CDRIVEHauling 10' pipe on a Trek Shift3

4,960
651
May 8, 2012
I wonder if we'll never know. The OP seems to have left the room without so much as a Ciao!

Chris

7. ### KrisBlueNZSadly passed away in 2015

8,393
1,270
Nov 28, 2011
He might just be busy...

8. ### CDRIVEHauling 10' pipe on a Trek Shift3

4,960
651
May 8, 2012
Busy? What is that?

Chris