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15. Wildcard

This week I worked with things that have not been covered in the Fab Academy: 1. low power electronics circuits, 2. solar power circuits and 3. intelligent circuits that don’t involve microchips and 4. miniature and extremely compact fablab made PCBs.

Here are the eagle files for the larger version:

1DOF tiny white solarbotics version v3 74AC240 OPTION 2 COMPACT even SMALLER.sch

1DOF tiny white solarbotics version v3 74AC240 OPTION 2 COMPACT even SMALLER.brd

Here are the eagle files for the super slim version:

1DOF TSOP20 expensive amazon motor 74AC240 v1 .sch

1DOF TSOP20 expensive amazon motor 74AC240 v1 .brd

Here’s the BOM:

low-gate-turn-on-voltage MOSFET (DMN2215UDM-7) dual package: ?€

74AC240 TSSOP20 format: 0,462 €

SMD tantalum capacitor 0.2F cap: 1,21 €

solar cell (4.46V KXOB25-01X8F or 2.07V KXOB25-05X3F-TR depending on how you plan to use them and the trigger you select): 3.56 € (1.78 € x 2)

micro gear motor: 4.25€

ISL88001 voltage trigger (this has replaced the 1381 used in the circuit, which has since been replaced with the MCP112): 0,356 €

standard 1206 SMD diode + 0.47uF cap: 0,1€

Total: 9.938€ + PCB cost

Prototype #1:

I’ve made the PCB for with the 74AC240 (THE AC IS IMPORTANT) based on this design from http://www.smfr.org/robots/robot_images/dualsolarhead_schematic.png :

The circuit combines a series of inverters to amplify current in one direction or the other through a motor depending on which solarpanel has more light. It uses a voltage trigger IC to fire. Here is my redrawn version of the circuit without the solar engine:

And here’s what my version looks like:

With all the components ready to solder:

Assembled the circuit is pretty small:

Next I tested some different configurations and motors.

This one is super tiny but badly proportioned:

With bigger gear motors:

With a different pair of shoes:

And a tripod in place of a llama’s body:

With solar panels facing the other way:

I then developed a more compact version of this circuit:

Prototype #2:

The TSSOP20 logic chips I ordered finally arrived and so I am now engaged in an attempt to make the circuit fit behind a single solar panel. I am using a new (and rather expensive - 15 euros) miniature gear motor I found on amazon.

I am using this lovely solar panel (3,4V @ 4,4mA) from digikey:

https://www.digikey.fr/product-detail/fr/ixys/KXOB22-01X8/KXOB22-01X8-ND/2754274

Here is the schematic in eagle:

And the circuit screen shot:

And the image to cut:

Don’t think I can get it much more compact in a fablab made version:

Here is the device assembled:

With a tiny 3D printed component to attach to the motor and hold the solar panel in place:

Again I tested various aesthetic options. This one is satellite inspired:

Here with two panels instead of photodiodes:

Here are a couple of videos of the machine, in its different configurations, working:

And the single cell version:

Last update: May 18, 2021