How do I reverse the motor in my circuit? - Page 1
Forum section: electronics / beginners

author: soheliadeep
author_rank: Newbie
timestamp: August 27, 2014, 11:11:25 am
content: I am building a humane rodent trap, and require assistance. The trap works using an LED (not shown) and LDR (photoresistor). When the rodent walks over the LED, The LDR increases in resistance and more current flows into the transistor. Then a buzzer, An LED and two motors turn on to alert the consumer. The motor cuts off entries and exits for the rodents. They stop spinning when the door activates a microswitch. The voltage out of the transistor is 3.6VHowever, I do not how I would wire it up. I know how to use a DPDT to reverse a motor, but I just made a mess when I tried.I need the motors to go in reverse using the 4.5V wire when the circuit receives an input.Switch off: Motors forward If dark using 3.6V supplySwitch on: Motors backwards regardless of light using 4.5VMotor Circuit:And How would I factor this modification into my circuit?

author: paul18fr
author_rank: Contributor
timestamp: August 27, 2014, 11:19:44 am
content: I think I saw something on that in

author: CoilKid
author_rank: Contributor
timestamp: August 27, 2014, 09:10:15 pm
content: Hello again, saw you on EE.SE. I believe you can just reverse the voltage, and the motors should reverse. I'm not sure how to do that in practice, with your circuit, but a switching system close the the battery would probably be a good bet.Good luck with the trap!

author: Bukurat
author_rank: Regular Contributor
timestamp: August 28, 2014, 07:10:19 am
content: Firstly I'm a little confused by your circuit so I've added a question to it. If the two switches I marked in my image are in fact the door micro-switches, there are better ways of stopping a motor than putting a short circuit across it.To reverse the direction of the motors you need an H Bridge. Here is one I found laying around on the intertubes.If you drive input A high and input B low the top left and bottom right transistors turn on allowing conventional current to flow through the path Q1, motor, Q3. Reverse the input and the path becomes Q2, motor, Q4

author: WarSim
author_rank: Frequent Contributor
timestamp: August 28, 2014, 07:31:07 am
content: Quote from: Bukurat on August 28, 2014, 07:10:19 am"need"? Really? You are going to tell someone asking for help he needs an H bridge as if it is the only option?Sent from my iPad using Tapatalk

author: Bukurat
author_rank: Regular Contributor
timestamp: August 28, 2014, 07:39:26 am
content: Quote from: WarSim on August 28, 2014, 07:31:07 amI'm waiting to see your contribution.

author: WarSim
author_rank: Frequent Contributor
timestamp: August 28, 2014, 07:46:48 am
content: Quote from: Bukurat on August 28, 2014, 07:39:26 amNo need to contribute apparently the method "needed" is an H bridge..If it has to be that way what contribution can be made.Sent from my iPad using Tapatalk

author: paul18fr
author_rank: Contributor
timestamp: August 28, 2014, 07:54:10 am
content: Quote from: WarSim on August 28, 2014, 07:46:48 amsee my previous post linking to the (good) tutorial of Afrotechmods ....

author: WarSim
author_rank: Frequent Contributor
timestamp: August 28, 2014, 08:19:15 am
content: See no H bridge. Used a relay because the op said they knew how to use a relay. Kept their sensor method cause they came up with it.Sent from my iPad using Tapatalk

author: Bukurat
author_rank: Regular Contributor
timestamp: August 28, 2014, 12:32:15 pm
content: I don't see any good reason to divert the OP's post to argue semantics with you but I see you have used an old school H bridge to reverse the direction of the two motors. We used relays in a similar configuration for DC motors back in the 1960's. Of course we had interlocks to ensure the motors were powered down before the relays energised. It doesn't matter if the switches are mechanical or electronic, the configuration remains the same.Rather than spoon feed the OP with a complete circuit I would rather point him/ her in the appropriate direction. I believe it's better to teach a person to fish.

author: SL4P
author_rank: Super Contributor
timestamp: August 28, 2014, 02:17:45 pm
content: I agree that an H-bridge is probably too much in this application, however - the limit switches in series with the motors makes reversing a moot point, as they will be open-circuit when they hit the first limit.Interesting to see which direction this thread goes!A small micro, or some simple diode-relay logic.

author: jlmoon
author_rank: Unknown
timestamp: August 28, 2014, 03:35:18 pm
content: My contribution:I see no problem at all using a widely accepted industry standard in directional control.. The awesome H-Bridge.. either using low Rds on HexFets or bipolar if you want to play cheap. From the initial post, I suspect the Op may not know as much as some folks on the board, I see the suggestions as a good starting path to learning something good!From what I can see the currents are so low with this circuit.. you could use almost any set of junk box NPN TO-92 devices and bit of decision logic and pull this one off.

author: WarSim
author_rank: Frequent Contributor
timestamp: August 28, 2014, 04:23:17 pm
content: Quote from: SL4P on August 28, 2014, 02:17:45 pmI agree. I see now that I forgot the reversing diodes. Oops.After all don't want to spoon feed.It was only to show one of the options. It is up to the author what road to decide which road to take. Nor am I going to explain the many design options.Sent from my iPad using Tapatalk

author: WarSim
author_rank: Frequent Contributor
timestamp: August 28, 2014, 04:27:48 pm
content: Quote from: jlmoon on August 28, 2014, 03:35:18 pmOf course there is no problem with using a full H-bridge. Or even a partial bridge. This tangent was because of the post that implied it was the only option.Sent from my iPad using Tapatalk

author: WarSim
author_rank: Frequent Contributor
timestamp: August 28, 2014, 04:32:53 pm
content: Quote from: WarSim on August 28, 2014, 04:23:17 pmOh I see your point. Well I was prompted for a contribution at 4AM. A bit more sleepy than I though.Would need independent reverse control or open limit switches. Depending on what the author wants. If the author want to use a relay at all.Sent from my iPad using Tapatalk