I have decided to try and put lights on my Parkzone Citabria. I wanted at a minimum wing markers that flashed. The process involved researching a light, low power circuit that could pulse 2 LEDs about once a second. In my research I found a site that describes a fascinating circuit that uses only a single transistor (and not even all the pins!) However, I was not able to recreate the flash as the voltage of the Citabria battery is only about 4V. However, in writing to Mr. Cappels, he offered a novel solution I had not thought of - microprocessor control. He generously programmed an ATTiny12 to flash 100ms pulse at 4Hz, plus a few others - which turned out to be a good thing.

Flashing at 50ms 2Hz turned out to be more eye catching. Before committing to anything, I first plugged the chip into a experiment board along with a number of LEDs to confirm power consumption, flash rate, circuit wiring etc. The resistors in line with the LEDs are all 150 Ohm - being from surplus they are different power ratings (not a real concern at the low power I am using - 0.1W).

The 50ms at 2Hz was the ideal rate, so the process of soldering everything together began. To save weight Dick Cappels suggested surface mount LEDs. I agreed - then I saw how big they are. SMT LEDs are small! Soldering them was to be a challenge.


To further save weight, I opted for enamel coated wire from a solenoid. This did not make the soldering process easier...

Soldering leads to the LEDs was the first major step. To begin with I unwound a length of wire and formed it into a loop as follows:

Then I stripped the enamel off with a small lighter (burn the enamel carefully, then wipe the ash off with an abrasive cloth). Here is the result:

Next I carefully wrapped the loop around the LED such that each side was wrapped around a contact:

I then carefully soldered the wire under a magnifying glass:

Then I snipped the excess wire from the loop leaving the LED at the end of 2 wires.

Once that was done, I tested the circuit - only having a few spare components to work with, I did lots of testing at nearly each stage. Here's the yellow LED blinking:



Once the yellow LED was complete, I repeated the process for the red LED. I also wired up a white LED direct to the power (via a 1K resistor) for a landing light. The power consumption of the complete circuit was very satisfying. Between blinks it is only a couple of mA. The flashing LEDs only draw around 40mA during the pulse.



That was satisfying - next, soldering the circuit. I opted to wire direct to the chip without using a socket. There was an increased risk of damaging the circuit, but again, I'm adding this to a plane that weighs 20+ grams! I'm nervous about what the extra weight will do. So I cut the unused leads and solder the components direct to the chip: