Hello,

I'm new to the electronics field. I've been doing simple projects on bread boards and have a very basic understanding of very basic parts and concepts. However, I don't know what I don't know, and just needing pointed in the right direction really. I'm not asking for answers, just direction. I would prefer to discover the solution myself so that I can really learn it.

What I'm wanting to do is create a circuit that will power on my amateur radio for me when my car turns on, and turn it off when my car turns off.

I know I need to tap into certain wires that will become hot when the ignition is turned on so that the circuit can sense that the car is on. And, to turn on my radio, I know I need to tap into the switch under the power button. This power button on the radio needs pressed for about a second for the radio to turn on, and pressed for about a second for the radio to turn off.

What kind of research terms should I be researching? What are circuits like this called? Is this even possible without an IC or Arduino/computer?

Help is very appreciated. Thank you.

 

This involves timing, and logic, so you need an electronic timer at the very least to pace the button press.

Is the radio powered by the car?
How would you prevent the radio and car from getting out of sync, so it turns the radio off instead of on?

 

Monostable multivibrator.

It can be configured to give a 1 second pulse on power up. Often implemented with a ‘555 timer IC.

Then you will need an electronic switch to actually activate the button. This can be a transistor or a relay. A relay will always work. The way you use a transistor will depend on how the power button is actually wired.

 

Sounds like a simple relay problem. Your rig is probably already wired and fused from the battery? To carry that power, you need a 12V relay powered from the ignition switch accessory circuit. I've even used a Ford starter relay to power higher powered circuits in the past. They used to be pretty cheap, grounded by bolting to the frame and can carry all the amps that a starter needs. Yeah, it's overkill but a cheap and easy solution. There are smaller automotive 3 prong 12V plug in relays but they require a base module also.

 

The radio is already installed & working, it's directly connected to the battery and fused on both the positive and negative lines.

 

I know I need to tap into certain wires that will become hot when the ignition is turned on so that the circuit can sense that the car is on.

What do you consider "car is on" to mean? Engine running or ignition in the on position?

This power button on the radio needs pressed for about a second for the radio to turn on, and pressed for about a second for the radio to turn off.

Why do you need a button press to turn it off? Wouldn't removing power accomplish that? Does the radio get confused when it isn't turned off with a button press?

If you don't need a button press to turn it off, you just need a one shot triggered by the application of power.

 

Older radios had a mechanical switch to turn on. Newer models have a button and electronic switching. Which means that newer models still have to be turned on after power is applied to them as they automatically power-off when power is removed from the radio. Getting into the radio power-on circuit for a newer model may be difficult...

 

The radios I'm using are Yaesu FT2900R.
I think powering off via removing power could work. But, powering on still needs the button press. So if I have to do that, I figure might as well turn it off with a button press.

I've got one that doesn't work anymore. I can practice taking it apart, try soldering to the power button, and learning what not to do.

 

Monostable multivibrator.

It can be configured to give a 1 second pulse on power up. Often implemented with a ‘555 timer IC.

Then you will need an electronic switch to actually activate the button. This can be a transistor or a relay. A relay will always work. The way you use a transistor will depend on how the power button is actually wired.

I have researched this monostable multivibrator - this is the right approach. I've found a lot of circuit examples for this, but only one that provides resistor and capacitor values. I've tried building the circuit on my breadboard 5 times now, can't get it to work as intended. When the small capacitor is discharged and the button is pressed, the led lights up for only a tiny brief moment. If the little capacitor is not entirely discharged, the tiny brief blink doesn't happen at all.

This is the circuit I've built.
http://www.learningaboutelectronics...le-multivibrator-circuit-with-transistors.php
The article says the LED should stay lit for about 4.7 seconds. If I apply voltage to the base of the B transistor directly, the LED does light up for about 2 - 3 seconds.

Are there any errors in this circuit diagram? It looks right to me, based on all the other circuits I've found for the monostable multivibrator, except that this one uses electrolytic capacitors and the others use regular capacitors and diodes.

 

dele

 

You may be able to do what you want with a small relay and a capacitor in series with the coil.

 

You may be able to do what you want with a small relay and a capacitor in series with the coil.

That's an interesting thought. I can see how that could work. But, that method would only work for vehicles. I'm a bit hooked on this monostable multivibrator idea because it can be used in places other than vehicles.

 

I have figured out how to build a monostable multivibrator per a schematic in a book I have "MAKE: Electronics third edition".

The big thing that I was stuck on for a long time with this method was the pin numbering on the 555. On the right, I had assumed it went from top to bottom 5, 6, 7, 8. But actually it's 8, 7, 6, 5.
Now, I'm trying to build this to emit a single pulse from constant power.
https://electronics.stackexchange.c...itch-momentary-pulse-output-when-switching-on

 

The above circuit only works if I take out the diode.

 

The circuit you found that does not work maybe was one of the millions of circuits on the internet from school kids who
live in a country with poor education.
The pin numbers are not shown and the diode causes it to not work.

Instead, you should look at manufacturers datasheets like these ones:

 

The diode, installed correctly, should not affect the circuit since it is always reverse biased. I think it is there to discharge the capacitor when power is turned off.

Did you install the diode correctly? if it is backwards it will stop the circuit from working.

 

And the first circuit is drawn incorrectly. There should be a dot, indicating a connection, where the wires cross above the collector of the transistor on the right. Did you make that connection? It is needed.

 

BobTPH
q1: I probably put it on backwards, now that I'm reading what you've said. I just tested the direction of flow on the diodes I'm using, and was extra careful to install per the schematic and it does work with the diode now.

q2: I did make that connection. I searched a lot about a monostable multivibrator. I found 4 or 5 different schematics of the same circuit, just with different style drawing. I don't want to give up on it. I just don't know what I'm doing wrong. It's probably something simple again. All the issues so far are simple and my fault.

 

For powering on the radio via the vehicle accessory circuit as @SamR described, I've settled on the below circuit. It's working on the breadboard.

I plan to control a small relay with the output pulse that is generated. The relay would be soldered into the power button of the radio. This circuit is based on the one above with a couple very minor modifications recommended in the book I have "Make: Electronics 3rd edition".

Measuring with my multi meter, this is using 66mA when the LED is on, and 35mA when the pulse is done.



Now, I'm trying to solve for powering off the radio when the vehicle accessory circuit becomes un-powered. Searching this site and others, I've come across two options: Depletion mode FETs and J-FETs.

References:
https://forum.allaboutcircuits.com/threads/closed-by-default-transistor-design.192531/
https://www.allaboutcircuits.com/te...hpt-5/junction-field-effect-transistors-jfet/
https://www.allaboutcircuits.com/textbook/semiconductors/chpt-5/transistor-switch-jfet/

I'm looking through my transistor assortment I have, and not sure if any of them are J-Fets. I'm leaning towards buying a pack of them. Looking on-line, they seem really expensive. Cheapest I've found is a pack of 20 on Amazon for $10 USD, but not sure if they will work or not. I plan to use a J-FET to power basically a copy of the above circuit when the vehicle accessory circuit is powered off, to turn off the radio. Clearly, I also I need a fused power lines coming from the battery for this circuit. Nned to figure out how to determine the right fuse size for that.

Am I on the right track?

Thank you immensely for the help here. I don't think I could figure this out on my own, with my extreme noobness.

 

This circuit is based on the one above with a couple very minor modifications recommended in the book I have "Make: Electronics 3rd edition".

I'm not a fan of that book or the schematic drawing style the author uses. Does he draw those unnecessary connection dots on the pins of the IC?

I have no idea what the circuit you posted is supposed to do. I pretty much have the pin functions of the 555 timer memorized, so I don't have to refer to your table, but that doesn't make it any easier to decipher what you've drawn. I'll redraw more conventionally and then comment.

What type of LED are you using? It might not be on long enough to be destroyed, but it should have a current limiting resistor unless it's designed to operate 12V. If that's the case, you should make a note on the "schematic".