Hi there community,

I have a doubt that I would like to share with you guys. In the attached photo I have a 555 timer running on astable mode, a circuit that I would like to be applied into a screen wiper concept.

The idea is that the engine could run in one direction, followed by an off time and after it started again automatically, it could run in the opposite direction, that is: turn right - stop for a few seconds - turn left and thus follow the cycle again .

In the photo (I used the Tinkercad online software) I can run the motor in both directions but I am unable to find a solution so that it can stop for a few seconds before reversing the direction.

I already tried with a DPDT relay but due to connection reasons (I am not an expert) of the relay with the circuit, I can't also make it work as I explained above.

Do any of you guys have a possible "user friendly" solution?

Thank you in advance.

Kika37

 

If the motor reverses in your actual circuit then your drawing is wrong. It shows both of the motor wires connected directly to the battery

 

Welcome to AAC!

In the photo (I used the Tinkercad online software)

Schematics are easier to read than cartoons. TO-92 transistors come in 3 different pinouts. Which one applies to the transistors you're using?

 

If the motor reverses in your actual circuit then your drawing is wrong. It shows both of the motor wires connected directly to the battery

Thanks for the input AlbertHall. Any suggestion then on how to re-make the connection?

Regards,
Kika37

 

As pointed out, you wired the motor wrong. It isn't connected directly to the battery, but the red connection is in the wrong hole.

Your cartoon with component designators used in the schematic.


Drawn more conventionally; with the motor connection corrected:

I couldn't read the terminal labels on the transistors, but could tell what you intended by the connections. It's easy to see why the circuit doesn't work.

 

Welcome to AAC!

Schematics are easier to read than cartoons. TO-92 transistors come in 3 different pinouts. Which one applies to the transistors you're using?

Thank you for your reply Dennis. I attached the schematics that I've based myself to. The difference on the schematics is that, on the simulation programe, i am not using a wiper motor but instead a 12V DC motor. Besides that, all the circuit connections follow the drawing.

Thank you again for your reply.

Regards,
Kika37

 

As pointed out, you wired the motor wrong. It isn't connected directly to the battery, but the red connection is in the wrong hole.

Your cartoon with component designators used in the schematic.
View attachment 203390

Drawn more conventionally; with the motor connection corrected:
View attachment 203391
I couldn't read the terminal labels on the transistors, but could tell what you intended by the connections. It's easy to see why the circuit doesn't work.

Hi there again Dennis,

I can't thank you enough! Very much appreciated to you.

Regards from Portugal!
Kika37

 

I attached the schematics that I've based myself to.

You haven't connected the transistors that way. Also note that T2 is a power transistor.

 

You haven't connected the transistors that way. Also note that T2 is a power transistor.

After you mentioned it I went to re-check and indeed I get to see the flaw on my transistors way of connection.

Again, thank you Dennis.

Regards,
Kika37

 

The idea is that the engine could run in one direction, followed by an off time and after it started again automatically, it could run in the opposite direction, that is: turn right - stop for a few seconds - turn left and thus follow the cycle again .

If this is intended for wiper motor, then the motor runs always in the same direction with reversal being done mechanically.
The '555 should just turn the motor on and off.

In the circuit diagram of post #5, the motor will never run as either Q1 or Q2 will be on, but never both.

 

After you mentioned it I went to re-check and indeed I get to see the flaw on my transistors way of connection.

Note that transistor T2 doesn't have a base resistor to limit current. That's done by R5.

 

Is that a switch, left center? If so then isn't it shorting plus to minus?

 

As pointed out, you wired the motor wrong. It isn't connected directly to the battery, but the red connection is in the wrong hole.

Your cartoon with component designators used in the schematic.
View attachment 203390

Drawn more conventionally; with the motor connection corrected:
View attachment 203391
I couldn't read the terminal labels on the transistors, but could tell what you intended by the connections. It's easy to see why the circuit doesn't work.

Thought the motor was supposed to be reversible. I don't see this motor running in reverse. Besides, D2 would be a dead short in (um) (reverse) direction.

When pin 3 is high, Q1 turns on providing ground path for the motor, but at the same time Q2 is off - so no motor power at all. When pin 3 is low, Q1 turns off and the motor, even though Q2 is on and providing power to the motor, won't run without a ground. The path from Q1C to Q1B and R4 would grossly limit the motor's ability to run at all. Unless I'm reading something wrong. And I've been wrong before. If wrong now - please be kind and instruct rather than find fault.

At best Q1 and Q2 form half of an H bridge. You'd need a full H bridge to reverse the motor. And no snubber diode. A cap and resistor snubber would be in order.

 

Besides, D2 would be a dead short in (um) (reverse) direction.

I was trying to guess intent from what the OP has wired. Once he posted the original schematic, things became clearer.

 

I was trying to guess intent from what the OP has wired. Once he posted the original schematic, things became clearer.

Yeah, I hate when we have to do that - extrapolate possible intent with insufficient detail. Often a fail.

 

Yeah, I hate when we have to do that - extrapolate possible intent with insufficient detail. Often a fail.

I was correcting what I thought were errors. I thought it was a failed intent attempt to implement an H bridge to be able to reverse the motor.

EDIT: corrected wording.