Pushbutton speed control

[ryukyu]

I am trying to make a fan control that has low, medium, and high speed settings.
The fan is a DC motor that will run at 1.5 (low), 3(med), and 4.5V(high). I will have a momentary pushbutton for on/off and for sake of design I would like to use a momentary pushbutton to change speed settings as such:

Turn unit on
unit will start in low
pushing the speed control momentary will increment in the pattern L-M-H-L-M-H...

I thought that using a digital pot may be the solution, but they usually have more than 3 settings and I do not want to have to implement a counter circuit to reset to zero after every transition from high to low speed. It seems that most button-controlled digipots also have very small current capabilities which seem like they would be susceptible to issues with back EMF.

Any suggestions?

 

[carmusic]

how much current is the fan?

 

[Boncuk]

Hi ryukyu,

I guess it's a small fan with low current.

Here is a schematic and PCB design for a fan not drawing more than 500mA of current.

The circuit contains a button debouncer (HCF4093) and a decimal counter (HCF4017).

I assume you also want to switch the fan off.

When energizing the circuit Q0 of the counter will be high. Since there is nothing connected the fan will be off. Pushing the button increases the counter output to Q1 (lowest rpm) and so forth until highest rpm at output Q3. One more button push resets the counter and the fan will stop.

R5 has to be dimensioned to have the motor start safely from stand still. R8 should be for medium speed. T3 has no current limiting resistor which should result in full fan speed.

The PCB design is purely single sided and measures 2.86X1.5inches.

Boncuk

 

[Maris]

I would go with some small Microcontroller design. They are cheap and you can program all fency logic - connect your buttons to one pins, then connect your fan through transitor or FET to some output pin and then program logic inside. Some of latest "cheap" Microcontroller development boards I tried are TI's MSP430 Launchpad and STM8S-Discovery, but of course ardiuno or PIC would work as well.

 

[ryukyu]

Thanks for the replies guys. I did not specify (as I should have) that I was looking for this to be fairly small. I am opting to use either a switched potentiometer (though I don't like the ability to stall the motor) or a four position rotary microswitch as shown.