First time building MSE, having problems

I bought a solar cell from that has a standard Miller engine etched onto it ( ), then I got my hands on some transistors and capacitors to use. I soldered everything up onto the board, hooked up my power capacitor and a motor. I have my multimeter connected to the leads of the power capacitor and I can watch the voltage climb up to 2.6V and then stop. Its my understanding that when it gets to this point, the circuit is then supposed to dump all that voltage into my motor, but nothing happens!

I'm wondering if the transistor I substituted for the 1381 voltage trigger is to blame. I am using a TC54VC2102EZB, which according to its datasheet is supposed to trigger at 2.1V. But like I said, I can see my power cap go up to 2.6V and nothing happens.

Here are the values I'm using for the rest of the circuit, and a picture showing how I connected things to the solar cell:

C1 = 4700uF

C2 = .47uF

TC54VC2102EZB instead of 1381 for voltage trigger

2n3904 transistor

Solar cell rated at 4.5V / 18mA.

Here is what my soldered circuit looks like:

Any help is appreciated!

It looks like you’re

It looks like you’re missing  a diode in there.  Without it the trigger doesn’t see ground.

Ah! I thought I read that

Ah! I thought I read that the diode was optional, but when I put it in I was able to get an LED to flash :slight_smile: Thanks!

I’ve noticed that when I measure the voltage across my power cap in standard fluorescent room lighting it tends to hover around 1.5V without climbing or falling, but starts to climb when I shine a flashlight on it. I’d like to have this thing work indoors, is there a way I can modify the MSE circuit to trigger at a lower voltage? I don’t know if I can get a 1381 with a low enough trigger voltage for that.

Or maybe I should just tell whoever I give it to to always keep it by the window?

I just thought I’d add…

When I tried to get my first BEAM bot to trigger a pair of 1381J MSE’s indoors it took 8.0V panels to make it work! Barely. That was with what I thought was decent incandescent lighting too.

Just figures for you to consider.