Reducing DC motor speed w/min components

Use a 3 position switch instead, centre-off.

So, let's see... the existing fwd/rev rocker switch; a new speed pot; and a new on/off rocker switch. Getting pretty crowded on this little dude.

My goal is to consolidate functions of the pot and one switch. It looks like I can do without a power switch if I use a CMOS 7555 timer. It draws less than 100uA and at this rate the battery (1Ah) will last about a year if left in its box on idle, w/o charging. Longer if I remember to pull the battery when putting it away.

I think I'm going to use this approach.

Um. I though you were intending to replace the orignal control system. Why would you add a new F/R switch instead of using (or replacing) the existing one?

The single existing on/direction switch simply connects the battery to the motor in forward polarity or reverse polarity. I want/need to keep that for direction control (and being quite custom fit, it requires a bit of a hack to replace it with anything). If I want a PWM solution, adding a (small) pot w/switch solves most of the problem: I get speed variation and with the switch I can short across the MOSFET for full speed (MOSFET only gives 90 percent, or so). But that requires the PWM circuit to remain running (it needs to be powered in order to fire the MOSFET, doesn't it). So another switch to turn it on/off? Pretty soon this screwdriver starts to look like some transport ship on an early Star Wars movie (the later ones look much sleeker, for some reason...).

So I've decided that since the CMOS 7555 uses only 100uA it will run for years from this 1Ah battery without turning it off. So that's the route I'm currently taking.

Now if I can only find a mini-size 500K pot with push/pull or push-on/push-off switch. Every parts house seems to have huge minimum orders for a Bourns PTR91 series w/switch or stopped carrying it.

Maplin in UK has another brand that might work. But patriotism, y'know... (c;

Why? - Why not just have the switch bypass the MOSFET completely?

For a single unit, it might be easier to salvage one from the junk box.

Which switch bypass the MOSFET? (By my count, we're talkin' about 3 switches. I lost track of which you mean...)

1. The original fwd-off-rev rocker, that's gotta stay. That is the current means to connect polar voltage (+ or -) to the motor.
2. Pot and switch (plan to locate and install): pot controls duty cycle for the PWM circuit. The switch bypasses the MOSFET when full-speed is desired....
3. No plans for a 3rd switch, but I mentioned that if I could figure out how to turn off the 555 (or 7555) easily, I'd do so. Unless I add a 3rd switch (which doesn't seem possible with the limited real estate -- both internal and external -- on this tool) I'm going to use a CMOS 7555 and let it run all the time.

Your junk box must be fuller than mine. Care to donate to the cause? (c: I was hopin' to find something useable from a dimmer switch at the hardware store (a mini push-on/push-off switch and pot combo). But the ones that aren't sliders (which most of them are) are full-size pots. Dang!

This whole thing is getting insanely complex. All you really need is a dial to set the PWM ratio (including down to zero), & a switch to set the direction. Using a switching pot to cut off all power when the tool isn't it in use is a good idea. A cute way to change direction would be to use an integrated H-bridge to drive the motor, & switch an inverter in or out of the PWM output with a simple SPST switch, or a single set of contacts on the existing switch. Do all that, & all you need to do is add the pot, & rewire the existing switch.

If you live in Melbourne, Australia, no problem. ;^)

Find or buy one of those cheap little portable radios. The volume control is typically a tiny 5K or 10K log pot with an integral switch. With careful design, one should be a good match for an RC time delay.