Introduction: Engine Temperature Sensor/Gauge With Wireless Probe for Classic Vehicles

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I made this probe for my lovely Çipitak. A fiat 126 car with a 2 cylinder air cooled engine under the rear bonnet.

Çipitak has no temperature gauge showing how hot the engine is so I thought a sensor would be helpful.

Also wanted the sensor to be wireless to get rid of routing a cable all the way to the back.

I thought of making the gauge (receiver) part with some kind of a digital-analog something display which will be powered from the usb socket on my car's mp3 player.

And wanted to make the receiving probe part with two temperature sensors and power it from 3-4 AAA batteries.

Step 1: First Circuit Tests

While designing my circuits i've came along a useful website which i've downloaded some sample code that works beautifully and wrote my own code by using some parts of that code.

here is the link from that site related to using a pic microcontroller with an oled display


here is the linkfrom that same site related to using cheap 433Mhz RF modules for communication among 2 pic micros.

the root address of the site is below which is full of very useful practical simple circuits as the name implies(I have no relation with the site owners).

the two strange named mp4 files are small video files showing the system while running.

Step 2: Circuit Design and Testing

I've used a pic 12F1822 microcontrollers each for the transmitter and the receiver part.

An oled display is connected at the receiving part to display the measured temperatures.

As the 1822 controller has a very low ram, only the basic functionality of the of the display is used to print blocks side by side to form 6 digital letters in total.

two 18B20 temperature sensors work at the transmitting side as the temp1 and temp2.

Temp1 is for measuring the main engine temperature and it runs every 6 minutes and checks the temperature. If the temp is below 50°C then the circuit does nothing and goes into sleep mode to wake up again 6 mins later.

Temp2 can be used to monitor the temperature of a second point on the engine or maybe the temperature of the batteries at the transmitting probe.

if Temp1 is higher than or equal to 50°C then temp2 is also measured, the transmitter module is turned on by the controller and both measurements are sent to the receiver. Then the circuit switches its timing to wake up every 30 seconds and goes to sleep again.

The circuit wakes up 30 secs later to the same measurements and transmittion and goes back to sleep repeating this cycle as long as the engine is hot.

if temp2 falls below 50°C then the circuit thinks that the engine is turned off and stops transmitting, switches its wake up timing to 6minutes and goes to sleep.

The power consumtion with 6V power supply (4 AAA batteries in series) during normal operation while transmitting is around 5mA while not transmitting it is around 3mA . In sleep mode the current drawn falls to 0.03mA. That is a consumption figure which could easily enable the circuit to run for months with the same battery set.

hex codes for the transmitter and the receiver side are attached.

Step 3: Receiver Side Prototype

I've made the prototype of the transmitting side as can be seen on the photos by using multi holed protoype board. Cut a usb cord to use as the base of the device and also the power supplier.

Step 4: Transmitter Side Prototype

Transmitting side is also made in similar fashion by using a small multi holed prototype board.

I've used an old mouse as the case of the transmitter and randomly thrown the circuitry inside and attached some magnets to stick it to the sheet metal oil sump of the fiat 126 without using any screws or other parts for attaching.

Step 5: 3d Printable Case Design

I've modeled the oled screen and the other parts in solidworks and designed an outer case for the receiving part.

any available case can be used for the transmitter even a mouse case is ok as you know. So i didn't design a special case for it. Here are the steps of the receiver case design.

STL files for 3d printing are also attached.

Step 6: 3D Printed Probe Case

I've made a 3d printed case for the probe

Step 7: Installation and Testing

installation was simple :D. The probe can be attached to any metallic surface so i've tried engine top first, then the side of the oil sump. It works ok in both locations.

my test print was made from PLA, So expectedly it got softer in hot temperatures. I will try ABS next time.

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