DIY low voltage/amperage trigger?

[TREETOP]

I searched first and found some interesting stuff, but I haven't found an answer so I'll ask.

I'll try to make this simple.
I'm toying around with a McIntosh double din head unit from a Subaru, it's in my Tahoe right now.
I made a conversion harness from the McIntosh 13-pin din cable to 4 RCAs and a turn-on (amp turn-on is in the din, power antenna turn-on is in the molex but is only activated by the tuner).

The amp turn-on wire is providing 11.5VDC, but it isn't providing enough amperage to trigger a regular Bosch relay.

I have a drawer full of relays, probably 50 of them. I've tried close to 20 different ones- Bosch, Hella, Chinese, P&B, Emitter, etc. No luck with any of them- I figured maybe one of the cheaper ones might trigger with less voltage or amperage, no dice.

It looks like a low voltage trigger might work, I found one for $12 shipped here:
Directed 55000 (DEI - 55000A) Relays and Switches Adaptors, Connectors, and Wire Terminals Car Accessories and Installation Car Audio and Video - Sonic Electronix

BUT, I don't want to wait for shipping, and I don't want to have my amps hooked to accessory or a switch while I wait to receive it.

I'm hoping someone knows a way to build a low voltage trigger device out of regular available components. I've got a bunch of miscellaneous capacitors, resistors, diodes, etc, and there's a Radio Shack about a mile from here. And I'm antsy right now and I need a project.

Any ideas?
THANKS DIYMA!

[sqshoestring]

I'm not an expert at this but seems you could run a mosfet into the relay, maybe an IRFZ44 they are very common about $1.50. Since a great many amps use them to switch the power supply 12v is no issue at all. They turn full on at 5v. Should be run the signal to the left leg, 12v supply to center, and right leg to your relay trigger (ground). You have to insulate the sink on it; it is the center leg (or attach 12v to that), or get the encapsulated IRFIZ44 I think it is. Or a tiny relay should work. Really just about any TO220 transistor should work for that, the trigger current should not be enough to heat it even. Only thing is if there is no ground bleed on the remote wire you would have to put a resistor on it, some mosfet do not shut off right away when you take power off them if nothing grounds the wire. Maybe a few hundred ohm I don't know, or it might not be an issue as I'm guessing that is what they are doing with it. Just make sure it does not get hot after a while, but relay coil should only be a fraction of an amp. An IRFZ44 would be overkill for that current.

[mjgonegm]

If I read your post correctly, you need a switched power source to turn on amps or to switch on a relay.

Again after reading your post I would assume you are getting the switched source for the HU, but it only works when the radio is used as a source.

My question to you is why not find a 12v Switched source from somewhere else in your car or Make a switch to turn the amps and or trigger the relay yourself. (I.e. 12v from your battery-fuse-manual switch somewhere in the cabin-Amps/relay)

[TREETOP]

Originally Posted by mjgonegm

If I read your post correctly...

You didn't.

[TREETOP]

Originally Posted by sqshoestring

I'm not an expert at this but seems you could run a mosfet into the relay, maybe an IRFZ44 they are very common about $1.50. Since a great many amps use them to switch the power supply 12v is no issue at all. They turn full on at 5v. Should be run the signal to the left leg, 12v supply to center, and right leg to your relay trigger (ground). You have to insulate the sink on it; it is the center leg (or attach 12v to that), or get the encapsulated IRFIZ44 I think it is. Or a tiny relay should work. Really just about any TO220 transistor should work for that, the trigger current should not be enough to heat it even. Only thing is if there is no ground bleed on the remote wire you would have to put a resistor on it, some mosfet do not shut off right away when you take power off them if nothing grounds the wire. Maybe a few hundred ohm I don't know, or it might not be an issue as I'm guessing that is what they are doing with it. Just make sure it does not get hot after a while, but relay coil should only be a fraction of an amp. An IRFZ44 would be overkill for that current.

I appreciate this.
From what I remember about FETs, it seems like they can be PNP or NPN, and can be used similar to a relay to have one device trigger another by configuring them different ways. College Electronics was a long time ago though.
I'll try to search online using the part numbers you provided, and see if I can come up with something definite as far as a diagram goes. I went ahead and ordered the DEI 55000 but it won't be here for at least a few days, likely not til next week. I'd like to monkey with this a little tomorrow and see if I can DIY something.

Thanks!

[mjgonegm]

so what are you trying to turn on using the relay ?

[TREETOP]

Originally Posted by mjgonegm

so what are you trying to on turn using the relay ?

3 amplifiers, an electronic crossover, and 2 temperature controlled fan circuits.

I use a relay on my turn-on rather than trying to run everything direct off the turn-on wire, as a head unit's turn-on lead is normally not designed to switch more than a couple things. When using a relay, the turn-on wire only needs a small amount of current to switch, this is a pretty standard way of triggering multiple amps/processors. This unit obviously has a very low current rating as it won't even click the relay, the 800PRS I removed today and the AVH-P4000DVD I used for a month of course had no problem.

It's the remote turn-on lead of the McIntosh head unit that's not providing enough current, it's a factory head unit from a special Subaru and I'm not using it with the McIntosh/Subaru amplifier which apparently doesn't require much to turn on. It isn't abnormal for a factory head unit to deliver less than 12V or less than 500mA to turn on a factory amp, which is why the low voltage trigger devices are available. I was just hoping to make a temporary one for the time being, because I like projects and learning is fun.

[mjgonegm]

thats what i thought or you were havung the POP issue. but in the end you are not pulling much current over that 12v switched line.

This brings me back to.......12v Switched source from somewhere else in your car or Make a switch to turn the amps and or trigger the relay yourself. (I.e. 12v from your battery-fuse-manual switch somewhere in the cabin-Amps/relay)



You could do something realy cool with this and use it as a manual relay. More simply put, input the code and your audio system is now active

Other wise the low voltage relay is still you best option.

P.s. what part of IN do you live by, I swear I saw a truck like that some where, and i love those rims NOW drop it 4 inchs and add a supercharger

[TREETOP]

If I dropped it 4" it'd be pretty close to stock height again. No thanks. It's a Z71.

[mjgonegm]

well 7' then, Honestly was suppose to guess? J/k

[TREETOP]

If anyone else has any input, or anything to add to what sqshoestring posted, I'd like to hear it.

Trying to keep this on topic.

Thanks!

[MarkZ]

I'm confused. Have you gone to radio shack and looked at their small little blue relays? They've got some that have like 300 ohm coils, I think. You could even grab a 5v relay and a resistor (voltage divider) and provide closer to 1kohms of resistance. Once upon a time I think they had solid state relays too that had high trigger resistances.

If that doesn't work, you could wire up an NPN bipolar to do it, but you'll have a Vbe drop. Or, you could grab a comparator (op amp) at radio shack which will present an even higher input impedance and should provide enough current to your devices to not also need a relay.

[TREETOP]

Originally Posted by MarkZ

I'm confused. Have you gone to radio shack and looked at their small little blue relays? They've got some that have like 300 ohm coils, I think. You could even grab a 5v relay and a resistor (voltage divider) and provide closer to 1kohms of resistance. Once upon a time I think they had solid state relays too that had high trigger resistances.

If that doesn't work, you could wire up an NPN bipolar to do it, but you'll have a Vbe drop. Or, you could grab a comparator (op amp) at radio shack which will present an even higher input impedance and should provide enough current to your devices to not also need a relay.

No, I haven't been to Radio Shack yet, I wanted to plan my attack first since the guys at the one by me are completely clueless.

I asked about a resistor network a couple weeks ago and the guy thought I was talking about a TV channel, I explained what I was talking about and he said "Oh I was an art history major, I don't know about that kind of stuff!".

I'm OK with some basic electronics stuff, I'm good with audio stuff, I can fabricate with some of the best in the business (and have), but the stuff you're talking about is all brand new to me.
"Small little blue relays" sounds like a good start, what I'm picturing needing is a relay that's easier to trigger than a Bosch, that'll still let me switch 12V on the output side. Is that what you're talking about? Would that 300ohm coil trigger easier (less voltage/amperage required) that a regular relay? What would be a good start as far as specs, for what I'm doing?

Thanks by the way!

[edit] Is this the one?
http://www.radioshack.com/product/in...ductId=2049716

[MarkZ]

Originally Posted by TREETOP

No, I haven't been to Radio Shack yet, I wanted to plan my attack first since the guys at the one by me are completely clueless.

I asked about a resistor network a couple weeks ago and the guy thought I was talking about a TV channel, I explained what I was talking about and he said "Oh I was an art history major, I don't know about that kind of stuff!".

I'm OK with some basic electronics stuff, I'm good with audio stuff, I can fabricate with some of the best in the business (and have), but the stuff you're talking about is all brand new to me.
"Small little blue relays" sounds like a good start, what I'm picturing needing is a relay that's easier to trigger than a Bosch, that'll still let me switch 12V on the output side. Is that what you're talking about? Would that 300ohm coil trigger easier (less voltage/amperage required) that a regular relay? What would be a good start as far as specs, for what I'm doing?

Thanks by the way!

[edit] Is this the one?
7-9VDC/12A SPDT Relay, Mini - RadioShack.com

Yeah, you want to look at the coil resistance of these things. The one you link to has a coil resistance of 500ohms. So 12v across that coil would cause a draw of I = V/R = 12/500 = 24mA, which is pretty low. I can't imagine your McIntosh would have problems with that.

The only thing you have to worry about is that it's usually a good idea to install a quenching diode across those leads too. It prevents high voltage spikes from reaching the McIntosh when it turns off. Install it across the coil reverse-biased -- so that the stripe on the diode is touching the POSITIVE connection on the coil and the other end of the diode is touching the NEGATIVE connection on the coil (ie. ground). You'll have to do a little soldering here. Many of the standard bosch relays have these diodes already built in.

Or find a bosch relay somewhere else that has a high coil resistance. Go to pep boys with an ohmmeter maybe.

[chad]

You could always just saturate a TIP101 or 102 transistor to provide a current buffer.