I want to make a circuit with a slow dc motor, a pot to change the speed of the motor.

Thread Starter

Aminnich

Joined Aug 6, 2015
26
hey guys, I am new to this thread, not necessarily circuits. I have took a clas in high school on this kinda stuff, but I forgot a lot of it. Now I'm starting a model train layout and I want to do something abnormal things to the layout (also saving some money) so here is my problem..... I want to make a circuit with a slow dc motor, a pot to change the speed of the motor, and a switch to change the dorection of the motor. Im using this for the turnouts. I have googled it, but haven't found anything, I don't even know if it can b done. Thanks for any help!!
 

nerdegutta

Joined Dec 15, 2009
2,675
Hi.

I think it can be done with this circuit:
dc-motor-controller.png
It is a 555-timer IC that generates the PWM (Pulse Width Modulation) and a switch to change the direction of the DC motor. With the PWM you control the speed of the motor.
 

Thread Starter

Aminnich

Joined Aug 6, 2015
26
Hi.

I think it can be done with this circuit:
View attachment 89757
It is a 555-timer IC that generates the PWM (Pulse Width Modulation) and a switch to change the direction of the DC motor. With the PWM you control the speed of the motor.
Ok, Ummm thanks but do I need a circuit board for that? Could I just use small bread boards under my train layout for that? Sorry I'm not knowledgeable with this kinda stuff
 

AnalogKid

Joined Aug 1, 2013
8,221
Everything shows is available in through-hole components to be assembled on perf-board.

R3 (33 Ohm) is too small. It will allow over 300 mA of base current. The BD139 might handle it, but the high base current will decrease the reliability of both the transistor and the 555. Increase to at least 100 ohms and see how things work out.

ak
 

#12

Joined Nov 30, 2010
18,167
could I buy it all at a RadioShack?
RS is basically out of business, but if you can find one, all those parts are common enough it is likely RS would have them. There are a lot of transistors which will fit in the BD139 position. Use at least 35 volt rated, 1 amp rated and don't worry about heat. It's a saturated switch. They don't suffer much from overheating. This one will suffer about 0.3 watts. Too much for a TO-92 transistor package, but a TO-220/TO-234 should work nicely.
 
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Thread Starter

Aminnich

Joined Aug 6, 2015
26
Im not sure what I want to do, I have a bunch of ideas I want to try, but im going to eventually probably going to need some kind of circuit. As for RadioShack, I have a 1 close to my house yet, not much in stock, but he can order stuff for me. Like I said before, I don't know much about this kind of stuff
 

#12

Joined Nov 30, 2010
18,167
There are several on-line vendors to mail parts to you, if all else fails. The decision point is about price of shipping vs high prices in a RS store.

mouser, jameco, digikey, to name a few.
 

#12

Joined Nov 30, 2010
18,167
No, the direction of the motor reverses when you energize the relay coil or de-energize the relay coil.
There is no connection from any potentiometer to the relay coil. In fact, I don't see any relay coil in the schematic. That will be another circuit which you have to add. It will probably be a SPST switch labeled, "forward" and, "reverse".
 

Thread Starter

Aminnich

Joined Aug 6, 2015
26
Also im goig to want to add LEDs to the circuit for the control panel, telling me which way the switch is facing for the track turnout... But that isn't as important
 
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