My two twin boys are pretty into Fireman Sam these days, so the red walking car they got when they were babies got an upgrade. Four blue self-flashing LEDs, a toggle switch and a 2xAA battery holder; everything bought cheap on eBay. And voila! A fire truck with blue emergency lights.

Underside of walking car

Initially I wasn’t sure that it would last long, they they might try to pull on the cables or that the battery holder under the seat would break. They do stuff all kinds of things in that storage compartment under the seat. But no problems, they seem to be fairly careful with it.

Batteries in storage compartment under the seat

The AA batteries are 1.5 volts, and with two of them in serial; that makes 3 volts. Which is what the blue flashing LEDs uses, so no resistors required.

On-off switch

They provide the siren sound themselves, yelling wi-wu-wi-wu while racing from fire to fire. It was a very inexpensive, quick and easy build, and has given the boys much joy 🙂

Here are the parts I used:

  • 1 × Battery holder, 2xAA, with wire
  • 4 × LED 5mm clear, flashing Blue, 3.0-3.4V, 20mA, 7000-8000mcd, 20°
  • 4 × LED holder 5mm, Chromed metal
  • 1 × Switch, toggle, 1-pole, micro, MTS-102, on-on, 6mm
  • 1.8 m Wire, stranded, 2-cores, 0.13mm2 (26 AWG), Red/Black

Last commit 2023-12-25, with message: replace emoji slight_smile/slightly_smiling_face