Modular 555 power cycler

Overview

As part of the final for Energy, Rashida and I are dealing with 555 timer circuits and intermittently power cycling a rover. For this class I’d like to create a modular 555 timer circuit that is A) adjustable in its cycle, and B) modular in its use.

Here are the schematic and calculations for the 555 timer circuit. Rashida uses a different configuration of the 555 timer, and is planning on allowing the resistors and capacitor to be adjustable.

I plan to sacrifice some of the adjustability in favour of a mostly SMD (and thus smaller) board. To allow for a bit of flexibility I will use a potentiometer as R2, and include two selectable capacitors.

Technicals

R2: As seen here, R2 affects the time off in relation to R1 (time on). Unfortunately with the basic setup the time off can never be more that 50% of the duty cycle. Rashida’s solution is to us an ‘improved’ 555 timer circuit, my solution is to use a logic inverter in front of the relay.

BOM

  • 47 uF capacitor
  • 470 uF capacitor
  • Transistor (or logic inverter)
  • 500K resistor
  • 500K potentiometer
  • Toggle switch
  • Relay

Three Battery/Cell Types

Last summer I tried my hand at building a drone. I learned a lot about drone battery use, and eventually settled on a 14.8V (4*3.7V), 4000mAh Lithium Polymer (LiPo) battery with a 10C rating

In my last job we occasionally would use the lead acid batteries you can get at most hardware stores. The standard size we used was 12V, 7Ah, C5 capacity.

I also often use CR2023 coin cell batteries that provide 3V and around .2 mAh. I’m not sure of the C rating.

Powering an LED (round 3)

Last semester I got really into powering my fabrication projects with human power. This in turn built off a project I made a year or so ago, a hand cranked LED sign. All of these were kind of hacked together, so I look forward to approaching energy generation in a more formal context for this class.

The projects mentioned above all use DC motors to generate power, so for this week’s assignment I asked the group if we could experiment with stepper motors instead.

It wasn’t difficult at all to plug in an LED to a 5V stepper and get it to turn on. The really surprising thing was that is didn’t seem to matter not only which direction you wired the LED (which makes sense as the stepper current alternates), but even which wires you plug it into. That was very surprising to me, I look forward to discussing how that happens more in class.