How to get 3.3v to 12v for a project??

[hittinswitches98]

Ok so basically the problem I have is I need to go from 3.3v dc to 12v dc. Here's whats going on. I have a Technologic Systems TS-7300 board that I am programming to. What I want to do is use outputs from the board to control 12v relays in a car which control valves for an air suspension. So basically in my program, when a user hits button 1 on the keypad, a pin on the board goes from active low (0v) to active high (3.3v). I want to be able to step the voltage up from the 3.3v signal to 12v so I can activate my relay which will then control the valve.

The relays are just 12v SPDT and are configured as follow:
pin 30 is +12v from the car
pin 86 is ground
pin 87 is my output which will go to the valve (12v)
pin 85 is my input from my board.

So basically I need to step up the voltage from 3.3v to 12v and I'm really not sure how to go about this. Can anyone help or give me some suggestions. The only thing keeping this from working is really that I don't know how to step up the voltage. The programming is all done and I've verified that the pins go from 0 to 3.3v then back to 0 upon a keypress, so that part is all done.

I have a ULN2003A that someone recommended to me, but I can't seem to get that to work. Not sure what I'm missing, but I appreciate any help anyone can give and if anything more needs to be explained, please let me know.

Thanks
-Scott

 

[blastronics]

all you need is a driver circuit.

ULN2003A thats for.

or you can you a single general purpose transistor to drive the relay.

 

[hittinswitches98]

This may sound dumb but what exactly do you mean by a driver circuit??

 

[blastronics]

You dont need to convert 3.3v to 12v.
what you need is to "control" 12V using 3.3V.

If I understand you correctly, please see this.

**broken link removed**

-blastronics

 

[Diver300]

A driver circuit, for example the ULN2003A, is meant for driving relays and similar loads. That is all it does. There are no control functions in a driver circuit. The output current and voltage of a driver circuit are usually much larger than the input current and voltage.

https://www.electro-tech-online.com/custompdfs/2007/12/uln2003a.pdf show you what the circuit does.

You should connect E to ground, and Com to +12V.

The inputs, 1B, 2B etc you connect to the board outputs that are at either 0 V or 3.3V

The outputs, 1C, 2C etc you connect to the relays. The other side of each relay you connected to +12V.

The ULN2003A shorts each of its outputs to ground when the corresponding inputs are high.

 

[hittinswitches98]

Ok I see what your saying here. So from my board I will go to 1B, 2B, and so on, then my outputs 1C and 2C will go to my pin 85 on my relay. So since the ULN2003A shorts each output to ground when the input is high, then I want to switch my program a little. So I would want to go from high to low, when would cause my ULN2003A to send 12v to my relay, therby activating the relay and switching my valve.

Does that sound right? Thanks so much for your help and for your time. I really appreciate it!

 

[Oznog]

You should be aware than automotive relays may require a significant current in the coil. This could translate into hundreds of mA, even amps, from the 3.3v line. This a driver as Diver300 suggests which switches existing 12v power from the external 12v supply is a better idea.