AutoTester Bill of Materials

1x Raspberry Pi ( – A cheaper Pi Zero W would probably work electrically, but I haven’t tried it.  The biggest risk is that when counting drops, the processor must capture as many frames as possible.  The pi zero is much slower and may not be able to keep up.  So I haven’t tried it yet.  The electronics case is sized for a full sized raspberry pi.  You also need a different camera cable for a pi zero since the standard camera cable doesn’t fit.

2x NEMA 17 stepper Motors (

1x solenoid (

2x electromagnets (

small disc magnets (

1x dosing pump (

1x pi camera with fisheye lens (

1x longer pi camera cable since the one they give you is really short (

4x wide angle white LEDs ( – You only need 4, but they seem to come in packs of 100

3x A4988 driver chips ( – They come in packs of 5

2x FQP30N06l Mosfet ( – This is a pack of 10, they may be cheaper/fewer alternatives

Buck converter ( – Another case where you only need one

13x 10ml syringes ( – 100pk

2x micro bearings (3x6x2) ( – seems to come in packs of 10

4x 1/4″ ball bearings (

2020 extruded aluminum cut into lengths of 1x 169mm, 2x 281mm, 1x 320mm (

The printed circuit board can be ordered from OSHPark (


Misc parts:
1x 2N3904 transistor
About 1ft of 3/8″ heat shrink tubing (used to give rubber padding for the stoppers)
7x 10k resistors 1/4 watt
1x 1.5K resistor 1/4 watt
2x 100 ohm resistor 1/4 watt
2x 1N4007 diode
1×2 x20 female stacking header
6x 1×8 female headers
3x 1×4 screw terminals (3.5mm pitch)
3x 1×2 screw terminals (3.5mm pitch)
1x 100uF electrolytic capacitor 50v
1x .1uF ceramic capacitor 50v
1x 12v power supply (probably about 4 amps to be on the safe side)
plastic tubing for in and out
6x M3 (or #4) self tapping screws (about 16mm or 3/4″)
10x M3 screws to attach the stepper motors and solenoid
20x M5-10mm screws to attach plastic to aluminum
20x M5 T-nuts

Other parts:

plastic trash can for cover (black suggested since you want it to be opaque, but you may need to paint it white or put a white can over it so it doesn’t bake the unit inside (if out in the sun).

Plastic tubing.  I used 1/4″ OD, 1/8″ ID.