Well, I think I've used up my annual brain allowance on this one. =\

I've got a 12v DC motor, two N.O. momentary switches, and a 12v power supply - pretty simple list of equipment. What I need to figure out (and get a parts list for) is how to get a circuit that will reverse the motor depending on which switch is pushed, with no power reaching the motor with both switches off.

Bullet point version:

• Button 1 = Forward
• Button 2 = Backward
• No button = Stop

My only stipulation is that I'd like to keep H-bridges out of it due to the cost of obtaining them - I have relays piling up like mountains around here, so a solution using them would be best.

Thanks in advance for the help!

EDIT: Sorry, I forgot to mention that I've searched the forums, but haven't been able to get anything definitive working in my head.

 

Here is one, however others exist with fewer relays:

http://www.zen22142.zen.co.uk/Circuits/Switching/reverse.htm

 

Thanks for the link, but I've seen that one before, and I don't have a third switch to put in the circuit, nor is it desirable in this situation.

 

You can use only two SPDT relays.

Connect the motor on the Commons.
Connect relay1 and relay2 NO to V+.
Connect relay1 and relay2 NC to V-.

 

What does your motor draw (I)?

 

The problem with using two SPDT relays is - unless I'm totally missing something - when the switches are released, the motor will continue to spin, not the desired application.

CDRIVE: If I recall correctly, 300ma.

 

Anyone got any sort of idea?

 

Hello,

Do you only need two pushbottons, one forward drive, one reverse drive?
Do you also need endstops?

Bertus

 

Here is a relay H-Bridge.

 

With only 300Ma current cant see why a H bridge IC is a cost factor as ive got probably 20 various types that handle 1 to 1.5A for free. They were obtained from older VCRs that were thrown out & there was usually 2 in each machine. All you need is the IC & your 2 switches.

 

Haha, this is why I'm glad you guys are around, because you think of things I totally miss.

I've got a couple old VCRs lying around, guess I just have a long way to go until I've got the right mindset to tackle harder stuff. I'll rip an H-bridge out of one of those and see what I can throw together with that. I'll report back on what I come up with.

 

Some to start looking for BA6209. BA6418N. M54543L. TA7267. To go in one direction on IC in pic, pull P1 hi motor goes in one direction while button pressed, release stops. Pull P2 hi motor goes in other direction & stops when button released. Warning dont bush both buttons at the same time will blow the chip.

 

The problem with using two SPDT relays is - unless I'm totally missing something - when the switches are released, the motor will continue to spin, not the desired application.

By now I'm sure that you've seen the link to Sgt.Wookie's circuit (posted by BillB3857) which clearly disproves that assumption. Less the limit switches, it's exactly what you asked for.

 

I figure it'll be a learning experience to go the fun route and try to rip an H-bridge from this VCR. Problem being, there's a ton of chips on this board, and none of them match the ones listed up above. I mean, there's gotta be one in here somewhere, right?

 

The machines i wrecked were 1990s vintage mutch newer ones may have one mounted by the motor driving the cassete cariage mechanism. I had a shed full of 1980s to end of 1999 machines to throw out but i chose to dismantle them for lots of usefull parts.

 

I'll dig around more inside today and look up datasheets at the very least. The two I have are both 1989, but I dunno if that makes much of a difference.

 

Do you have manufacturer & model Number?

 

Okay, sorry it took so long, but life happened and I had no time to sit around and pull chips. The closest thing I've found so far is an AN3814K motor driver IC (datasheet attached as image). I don't know if this'll do it (I don't see how), but I tend to miss things when we start to delve into ICs. There's also more ICs whose function I haven't determined in the second one, but one VCR I know for a fact didn't have an H-bridge IC, or anything that turned up even as similar.

 

If you happen across an L272, L2722, or KA334 - they are power opamps that could be used as an H-bridge for a low-power application like yours.

You'll get some loss of power due to the saturation voltage of the opamps' output.

ST Microelectronics' datasheet for the L2722 has a schematic for microcontroller control of a small DC motor:

You could do something similar with switches instead of microcontroller inputs.