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Solid state turn on device

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djunified

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Hello everybody,

I am utilizing the factory power antenna circuit in my car to act as the remote turn-on wire for my aftermarket amplifiers. I need to keep the factory radio because it is integrated with the climate control, and it would be too much work to integrate an aftermarket deck.

Anyways, the power antenna circuit seems to have no capacity for amperage at all. It is in fact a 12v dc signal according to my multimeter. I also checked how many amps the power antenna itself draws from this wire, and 0.00a registered on the multimeter when switched to DC amps.

I've tried numerous 12V pc style relays with coil resistances from 90 ohms up to 720 ohms. 720 ohms at 12 volts is about 200 milliwatts or 17 milliamps. That little amount of current is still too much for the factory circuit to handle. The relays didn't make a sound when hooked up.

I think Ford designed this circuit to cut mass-production costs. The power antenna module uses some sort of solid state device that reads the signal and raises and lowers the antenna based on when the radio is on or off. Thats exactly what i need to control my amplifiers, except the current capacity just isnt there. Not even using a 700 ohm relay.

I'm not familiar with solid state devices, so maybe you guys can help me.
 
A schematic of the antenna circuit would be helpful :)
 
Here ya go :p

As seen in the image, the wire that i'm tapping into would be the red/pink wire.

pwrantenna.jpg
 
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A ULN2004 https://www.electro-tech-online.com/custompdfs/2013/03/ULN2003.pdf would likely work for you.

It's a bit strange of a chip. It contains 7 relay drivers. The relay would be connected to OUT1 and +12.
The COMMON (Free wheeling) point also gets connected to +12 generally at the relay.

Anytime you use a relay, you should place a diode (so it doesn't conduct) across the coil just like it's shown in the IC diagram. The chip, connects the relay coil to ground.

To make the IC a bit more reliable, it might be a good idea to add a few more parts. A bypass cap, a transorb and a reversed biased diode and a small fuse. The automobile electrical environment is really bad.

You could do a quick test with a LED and resistor for the relay coil and go from there. I can look around to see if I can find an automotive qualified part.

We can only hope it's not a communications channel with a protocol.

By 12 V signal, you mean it goes to battery voltage when om and near ground when off?
 
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Yes by the 12V signal i'm talking about, the circuit goes 12V when the radio is on, and down to 0V when the radio is switched off.

I looked at the diagram for the ULN2004, and honestly I have no clue how I would hook it up for my application. I'm sure it will work if you guys say it will, so i have confidence in it. Only thing is the wiring.
 
You would only use one device. Let's call your relay coil pins A & B.
Pin 1 (IN 1) - Goes to the turn on signal
Pin 16 (Out 1) - Goes to Relay Coil Pin A
Pin 8 (GND) - Goes to Ground
Pin 9 - Goes to Relay Coil B
Relay Coil B to +12, fused, like at 1A or so.

Now the only thing I would worry about is the automotive electrical system killing the device itself, so we should add two more devices to help that.

A 1N4004 or 1N4003 https://www.electro-tech-online.com/custompdfs/2013/03/ds28002-1.pdf . Note the band on the diode. The band will point to + and the other end will go to ground. This will protect against the polarity being reversed and somewhat negative spike from the ignition system.

I'll look for a surge suppressor. What is your general location? US, uk etc. so I can recommend a parts source.

Also add a 1 uF Metalized polyester, 50 V capacitor across the power leads as well.

You'll need a PCB breadboard and a case to put it all together and the usual soldering supplies like soldering iron, etc.

If you want, you can test your circuit using one of these: https://www.sparkfun.com/products/10430 To avoid possible chip damage without the protections, don't start the car. Chip damage is unlikely, but possible. It turns out that the car may have +50 V positive spikes and -200 V negative spikes on it when running.

If you wanted to get fancy, you could add a LED and use screw terminals inside. A normal LED series resistor is sized by R <= (12-Vf)/.010. 12 being the voltage, Vf is the LED forward voltage usually about 1.2 to 2.1 V and the current, which is usually 10-20 mA. I used 10 mA. 1/2 Watt would be fine.
 
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Thank you. Now I have a better idea since you explained it fairly well. I am located in Canada, and I have access to a good electronics supply store about 30 mins from here.

The automotive electrical system does in fact see differences in voltages depending on load, engine speed, etc. That being said, you said it would be a good idea to also include a diode and a capacitor. If I understood right, I have to connect these two items across Pin 9 (Relay Coil B) and Pin 9 (GND)? So in sense I will be connecting Relay Coil B to both Pin 9 on the IC as well as my 12V battery source?
 
Not exactly.

Think of power conditioning to be a fuse, a reversed biased diode to ground, an 18V TVS diode or ZNR to ground. This then becomes the power source for your device. Your new, conditioned +12 V.
 
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I kind of got lost on what you said in your last post :p. Sorry if i sound like a total noob.

I will probably use Newark as my supplier, and i found the IC, diode, and capacitor on there. Here are the links:

IC - **broken link removed**
Diode - **broken link removed**
Capacitor - **broken link removed**

I know I also need a breadboard, but will these cut it?
 
So if i use the unidirectional TVS diode, it will work better than the 1n4004 diode that you mentioned earlier? What would be the appropriate pins to connect the diode and capacitor across?
 
Alright i will be purchasing those three items in multiple quantities just to be safe.

So in reality, the ULN2004 would be safe by itself if there were no voltage spikes at all? Lets say i didn't connect the diode and capacitor. Would the chip go up in smoke?
 
the OP said:
So in reality, the ULN2004 would be safe by itself if there were no voltage spikes at all? Lets say i didn't connect the diode and capacitor. Would the chip go up in smoke?

Nope. So, the quick test is to use the ACC position with the chip, a diode and a LED.

There are two diodes. One protects against negative transients < 0.6 V and the other positive ones greater than 18V. The 1 uf capacitor just tends to filter a little bit.
 
Nope. So, the quick test is to use the ACC position with the chip, a diode and a LED.

There are two diodes. One protects against negative transients < 0.6 V and the other positive ones greater than 18V. The 1 uf capacitor just tends to filter a little bit.

Whenever you say diodes, are you talking about the diodes that are contained within the chip itself? If so, i will go ahead and place the order for the parts and assemble the circuit when the parts arrive.
 
The chip, which is designed as a relay driver, places a diode across each relay that the chip drives. When a relay releases, since it is an inductor, stored energy gets released as a pulse. The diode forces that pulse back through the relay coil instead of the electrical system.

Transient suppression is an art. In one case there is prevention and the other case there is suppression of known causes.

A lighting strike to a home power line is rare, but it will take out many things in the home. The cost to install a whole hose surge suppressor might exceed $1000 USD whereas a ISOBAR surge suppressor will cost about $100 USD and comes with at least a $50,000 USD connected equipment warranty. It's not worth buying a surge suppressor without a warranty.

This is also something you should consider: https://canada.newark.com/multicomp...rd Terminal Blocks&MER=PPSO_N_P_Standard_None

and this: https://canada.newark.com/vector-el...lar Products&MER=PPSO_N_C_EverywhereElse_None

and a small case and grommets.

These: https://canada.newark.com/vector-electronics/t42-1-c/terminal-push-in-pcb/dp/38F1363 make life easier, but are not essential. The insertion tool is quite pricey, but you don't need it.

This wire: https://canada.newark.com/ok-indust...lar Products&MER=PPSO_N_C_EverywhereElse_None It's not essential, but the dispenser contains a cutter and stripper which is really convenient. Nonetheless, you need some sort of solid wire, like 22 AWG or smaller to make connections. Multiple colors, again, add to the cost of one.

Newark doesn't have a machined pin DIP socket, but this **broken link removed** can work. You have to cut it into two 8 pin sections. From experience, you normally loose one position.

So, while I'm at it, you may also need spacers or standoffs for the PCB. A hardware store may be aa source for a few unless the box contains them. Most of the time you have to buy 100 screws for the boxes.

Even for a simple project, the complexity adds up. The case, power supply, real estate (the PCB itself) and connectors add up quickly.

What about mounting? You can purchase flange mounted cases. I like these guys: https://www.polycase.com/index?

You should make sure it works first, but it should.
 
I just got all the parts in today. When i get home i will proceed to begin assembling the circuit on the pcb. Among the parts ordered, i did buy the TVS diodes and the capacitors. When im putting the circuit together, where should i be placing these items?
 
"where should i be placing these items"
Place them inside the passenger cabin. The tremendous temperature excursions, humidity, vehicle fluids, etc, create havock on electronic circuitry unless you specifically address them.
 
Take a 12 V supply and fuse it at like 1 amp. then put the cap, diode and TVS in parallel. The diode bands toward +12. Connect the other sides together and to car ground. The idea is if the device should be connected backwards or a surge is way too high, the fuse will blow.

@ST
It's not critical that the radio work under all temperature extremes from -40 to +125.
 
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