Good afternoon

I've got a small question here I hope is easy to solve If possible I'm looking for an electronic schematic for a simple and small method of controlling the speed of one of those small 3V hobby motors (those ones you usually get in cheap toys). The idea is a touch button that when you push it once it goes at 1/3 speed, next touch does 2/3, next is full power and then final press turns it off and cycle that all over again. Sort of the same idea you get for those small led head lamps or flashlights. It doesn't even need to be 3 stages it can go from 1/2 - full - off if that would work too. The power supply is also just a 3.5V Li battery. I'm trying to avoid using any kind of switch or knob as I just want to press one button. Anyone got some ideas?

Much thanks in advance to anyone who gives this a look. Gordon

 

Simple microcontroller setup as PWM feeding a FET.
Drive the gate with an NPN for light loads, FET driver for higher power.

 

A micro is easiest with minimum components, or you can do it with a 555, and a cd4017 clock.

 

Or '4017 to count button pushes. Outputs of the '4017 to switch resistors for a '555 astable circuit to generate the PWM then drivers as in post #2.

DD beat me to it.

 

Good afternoon

I've got a small question here I hope is easy to solve If possible I'm looking for an electronic schematic for a simple and small method of controlling the speed of one of those small 3V hobby motors (those ones you usually get in cheap toys). The idea is a touch button that when you push it once it goes at 1/3 speed, next touch does 2/3, next is full power and then final press turns it off and cycle that all over again. Sort of the same idea you get for those small led head lamps or flashlights. It doesn't even need to be 3 stages it can go from 1/2 - full - off if that would work too. The power supply is also just a 3.5V Li battery. I'm trying to avoid using any kind of switch or knob as I just want to press one button. Anyone got some ideas?

Much thanks in advance to anyone who gives this a look. Gordon

Hello there,

There are two basic versions of a speed controller. The first is just a feed forward type design, the second has feedback to control the motor speed even when the motor is under load. So we have two basic types:
1. Motor drive only which varies the current/voltage to the motor.
2. Motor drive with feedback to keep speed constant even under load.

Do you need #2 above or can you get away with #1 above?

#1 is simpler but the motor slows down when a load is applied to the shaft. #2 requires a little more circuitry but the motor does not slow down when a load is applied.

 

The circuit below was designed for provides about 50 mA for motor, because the output current of CMOS ic is too less, so I used the driver circuit as darling circuit, but the output voltage is more lower.

 

The circuit below was designed for provides about 50 mA for motor, because the output current of CMOS ic is too less, so I used the driver circuit as darling circuit, but the output voltage is more lower.

View attachment 158229

Hi,

I would prefer a voltage follower output stage so we have more predictable control of the unloaded speed. Might be hard to obtain though with only a 3.5v supply voltage.

 

Hi,

I would prefer a voltage follower output stage so we have more predictable control of the unloaded speed. Might be hard to obtain though with only a 3.5v supply voltage.

If you means that the voltage follower is using bjt then the output voltage will be as Vo = 3.5V-0.9V = 2.6V, that is similar with the output voltage using standard darling circuit in my circuit, if it is two stages then the output voltage will be more less as Vo = 3.5V-1.4V = 2.1V, I didn't use the voltage follower very often, because the output voltage will be loss about 0.9V, but I like to design the output voltage is close to Vcc when the output is high and close to Gnd when the output is low.

Use a 555 as pwm motor speed control can be get a big range speed control.

 

If you means that the voltage follower is using bjt then the output voltage will be as Vo = 3.5V-0.9V = 2.6V, that is similar with the output voltage using standard darling circuit in my circuit, if it is two stages then the output voltage will be more less as Vo = 3.5V-1.4V = 2.1V, I didn't use the voltage follower very often, because the output voltage will be loss about 0.9V, but I like to design the output voltage is close to Vcc when the output is high and close to Gnd when the output is low.

Use a 555 as pwm motor speed control can be get a big range speed control.

Hi,

Yeah the base emitter drop gets us in trouble with the voltage follower, not as bad with common emitter. Common emitter stage collector voltage is harder to predict though.
Maybe a Zetex transistor.

 

Use a 555 as pwm motor speed control can be get a big range speed control.

Yep. Better relationship between the control voltage and speed.

 

Hi,

Yeah the base emitter drop gets us in trouble with the voltage follower, not as bad with common emitter. Common emitter stage collector voltage is harder to predict though.
Maybe a Zetex transistor.

I haven't use the Zetex transistor yet, maybe hard to buy in the local EE stores, I just checked the one ZXTN25060BZ and the Rce(sat), Vce(sat) quite low, there is a little like to use the MOSFET.
ZXTN25060BZ 60V, SOT89, NPN medium power transistor

 

Yep. Better relationship between the control voltage and speed.

The easy way is to use the diode and capacitor to converts from pwm to voltage, but the problem is that the duty cycle changing too large, so it needs to use the switch to change the different capacitors, and maybe that is not what the TS wanted, if use other components maybe will causes the cost too high, do you have any good ideas to complete what you mentioned?

 

Circuit in post #6 provides the four voltage levels. Then use that voltage to change the duty cycle of a '555. Then drive the motor via a CE transistor from the '555 output.

 

Circuit in post #6 provides the four voltage levels. Then use that voltage to change the duty cycle of a '555. Then drive the motor via a CE transistor from the '555 output.

That was what I replied to MrAl in post #8.

 

That was what I replied to MrAl in post #8.

So we agree - that's good.