How to wire small AA battery project

[Reloader]

Hoping someone can help with this small little project. I reload ammo and I want to make what is known as a "vibrating powder trickler", basically a funnel that fits into a hole in a small aluminum block (roughly 3/4"x3/4"x2"). The end of the block has a hole that meets the vertical hole where the funnel mounts. A long 1/4" aluminum tube fits into the end hole. Under the bottom of the aluminum block a small cellphone vibrating motor is attached. The block is a vertical hole on the back side that slides over a wire mounted in a weighted base and a thumv screw allows you to raise and lower it. The device is also mounted at a slight angle so the powder will trickle down the tubne under vibration. The idea is to pour powder in the funnel, then using an intermittent switch, the cellphone vibrating motor causes the powder kernels to vibrate down the tube and into the weighing pan. It is typically powered by a pair of AA batteries. To make the device more effective, two switches are used. One switch draws power only from one battery to get 1.5v, the second switch will draw power from both batteries for 3v so you have a "slow" speed for trickling individual kernels of powder at a time and a "fast" speed so you can trickle more volume quickly to get to your target weight sooner.

The two little buttons (sourced from Amazon) each have two poles for attaching the wires. The batteries are housed in one of those little project battery holder/pack things. The vibrating motor is also two wires. How would I attach the wiring to the two switches and the battery pack so one button uses power from just one battery and the other button draws power from both?

 

[Lucien Nunes]

Battery negative to motor negative.
Battery midpoint (connection between the two cells) through 'low' switch to motor positive.
Battery positive through 'high' switch to motor positive

BUT

I don't recommend this as pressing both buttons at once will short-circuit one of the cells and possibly burn out the switches. I would rather have a changeover switch to select the speed, or use a changeover pushbutton for one of the speeds, or a 3-position spring-loaded toggle or rocker switch that you push one way for fast and the other way for slow, any of which would avoid the short circuit problem. You could also fix it with a diode in the mid-point connection, but even a schottky diode that has low forward voltage would lose a significant chunk of the available 1.5V and might not leave enough for the motor.

I've no idea whether it has any impact on the power being conveyed but don't forget that small brush motors and switches both produce sparks.

 

[Reloader]

Battery negative to motor negative.
Battery midpoint (connection between the two cells) through 'low' switch to motor positive.
Battery positive through 'high' switch to motor positive

BUT

I don't recommend this as pressing both buttons at once will short-circuit one of the cells and possibly burn out the switches. I would rather have a changeover switch to select the speed, or use a changeover pushbutton for one of the speeds, or a 3-position spring-loaded toggle or rocker switch that you push one way for fast and the other way for slow, any of which would avoid the short circuit problem. You could also fix it with a diode in the mid-point connection, but even a schottky diode that has low forward voltage would lose a significant chunk of the available 1.5V and might not leave enough for the motor.

I've no idea whether it has any impact on the power being conveyed but don't forget that small brush motors and switches both produce sparks.

What about a single push button with a small potentiometer? If that would work I think I'd like that arrangement better to give finer and more variable vibration so it could be "tuned" depending on the type of powder being trickled.

To give you an idea of what I want to do:

 

[Lucien Nunes]

You can vary the speed with a variable resistance (no real need for a potentiometer) but it might make the speed less stable and dependent on torque. A little PWM motor speed controller? (yes probably overkill!)
This looks suitable: DC motor speed controller

Check the specs for suitability, this was just the first example my search hit.

 

[Reloader]

You can vary the speed with a variable resistance (no real need for a potentiometer) but it might make the speed less stable and dependent on torque. A little PWM motor speed controller? (yes probably overkill!)
This looks suitable: DC motor speed controller

Check the specs for suitability, this was just the first example my search hit.

That looks like the ticket! Amazon has them for cheap enough ($8.29 for a pack of 3). I assume I would just wire the button switch on one of the motor leads, or on the battery side?

 

[Reloader]

That looks like the ticket! Amazon has them for cheap enough ($8.29 for a pack of 3). I assume I would just wire the button switch on one of the motor leads, or on the battery side?

One last question. I am thinking a power switch might be a good idea. Can I just put a 2-pin on/off rocker between the positive lead from the batteries to the PWM, and then an intermittent push button on one of the leads from the PWM to the motor so I can pulse it?

If I put the intermittent between battery and PWM, will that cause problems with the PWM getting intermittently zapped repeatedly? If I hook the batteries straight to the PWM and only have the intermittent button going to the motor, won't the PWM drain the batteries?

 

[Reloader]

OK, it is done. I didn't need to wire in an on /off switch as the little PWM module has it built in! This is a quick first test on a prototype I threw together. Decided on on some light cheap wood (basically cut of the end of a cheapo Home Depot 2x4) for the main body. Needs a few tweaks (more down angle) so the high speed will trickle out more powder quicker.

Thanks for the help.