Why I made this:

To help pilots who don’t have the money, or who can’t justify the expense of a full engine monitor, get CHT and possibly EGT data for each cylinder, and enjoy the safety benefits others have.

Basic idea:

Use an arduino/ redboard computer to read several thermocouples, and send the data via bluetooth to a smartphone in the pilots hand.

Basic steps to build:

Order parts

Solder pins and/ or wires on bluetooth module (so it can be attached to shield)

program arduino/ redboard with software to read shield using usb cable (use the free arduino programming software, also allows you to select how many thermocouples to read, and view serial stream, make any other programming changes you want)

attach thermocouples to shield

slide the shield, redboard/ arduino, and bluetooth module together

power up and check serial stream on computer first, there should be a repeating readout of the temps of each thermocouple.

Install redboard and other parts in a simple enclosure (modify as needed), add usb cable to power unit

install android app on smartphone to read bluetooth data (any serial terminal app can be used for testing/ datalogging, if desired)

test unit, then close up enclosure, test again.

install snap hooks (of my own design) to end of thermocouple wires so they can be slid into the stock CHT probe locations

go to aircraft, find a spot near the rear of the engine to secure enclosure box, then slide thermocouple probes in each cht location

attach battery, open app, go flying

finish flying, remove battery, go home, recharge battery

Here’s a pic of the basic parts, Ocean Controls shield (green) with thermocouples and bluetooth module attached, and sparkfun red board (if you’re not generally familiar with what these items are/ do, spend some time reading at sparkfun.com or google):

The only soldering here is to add some pins to the bluetooth module. I wire-wrapped wire around these pins (they can be soldered directly, but will break off if flexed much, whereas wire-wrapping is much stronger), then added a male header pin to the other end. This lets the bluetooth module plug right into the top of the shield. The shield and red board can be ordered with headers and pins, which makes them stack right on top of one another.

All together, placed in a plastic enclosure, they look like this:

The white mini usb cable will be used for power when installed.

I’ve made several of these monitors, and found them to be quite rugged and accurate. They are not sensitive to voltage, running on anything from 5-12 volts or higher, depending on the arduino. They do use some current, a 9v battery will only last about 1.5 hours. A cell phone booster battery will last for days. I made the first few with the battery and system all enclosed together; however I found this could be difficult to attach in the engine compartment as the enclosure required was fairly big. I much prefer the smaller enclosure, and a usb cord run to the battery, very simple and easy to swap out/ recharge.

Testing and programming on computer are easy, download the sketch from ocean, adjust the number of probes in the code and upload it.

A bigger enclosure that could fit everything inside, running an arduino mega. Red Velcro ties hold it to the engine mount:

Creating a basic app with MIT app inventor 2. I’m not the best at this, but did get it to function:

If anyone wants to see in detail, I’ll add them later.

Screenshot of the finished app in flight!

That’s all for now, email with questions. I’ll try to make a video one day soon of the device in flight.