Delta5 is a great open source laptimer for miniquads. It uses readily available components and costs a fraction of the price in comparison to commercially produced laptimers.

https://github.com/scottgchin/delta5_race_timer

As the Delta5 only has one published pcb design which only supports 4 receivers, I designed my own to fit 8 receivers. The only difference is that my design uses arduino minis in order to fit within a 100x100 pcb footprint, crucial for low pcb prices.

Step 1: Parts

You will require the standard components for this PCB other than the arduino minis and regulators. There are multiple types of layouts for the arduino mini, so make sure you get the ones with A4 and A5 pinned out the same as the ones in the pictures. I used 1/2W metal film resistors available from jaycar.

24 x 1K resistors

8 x 100K resistors

8 x RX5808 with SPI

8 x 20*20mm heatsinks

2 x MP1584EN DC-DC converter

8 x Arduino Minis - the PCB is only designed to work with ones that have the A4 and A5 pins broken out beside the main row of pins. These are the i2c comms and are necessary for communication to the raspberry pi

1 x PCB

208 x male/female 2.54mm headers

+ raspberry pi and wires, case if necessary

Step 2: PCB

The PCB can be ordered from any pcb fab company, the eagle and gerber files are attached.The F3D file is also attached if you wish to design a case for it.

Step 3: Assemble the PCB

Solder the resistors first. The resistor that is further away from each pack of 3 is the 100k. The packs of 3 are the 1k resistors.

The silkscreen is done so that the side that it is on is the side that you should put the headers in. Each of the arduinos require 12 pins on each side and 2 for the i2c pins. The receivers require 9 pins on one side and 3 on the other. Take care when soldering the 3 pins of receiver 2, as it is in the middle of the 3.5v regulator on the other side. This should remain as flush as possible so that the regulator can be surface mounted for heatsinking.

Adjust the regulator voltages to 5v and 3.5v before you install them. These can be reflowed on or just soldering using some more pins. Try to keep the back of the module touching the PCB so that it can at least have some heatsinking effect.

Solder pins onto the receiver modules and the arduinos. Using thermal glue, glue the heatsinks onto the receivers. It does not matter which number port you plug them into as it is just 8 modules(receiver and arduino) that have paralleled communications(i2c).

Having the modules on header pins allows for easier soldering and also replacement if any are faulty or experience an issue. Cheap arduinos can fail for no reason. Flash the arduinos with the same firmware as the one available on the github page, just make sure to change the target to arduino mini and also change the i2c address for each one.

The raspberry pi is wired up the same as the diagram on github. The regulator can power the pi with no issues.

The receivers do get quite hot even though they are being run on 3.5v so you may want to install a fan.