 | Home > In Car Electronics > Temp. sensor. A different approach |
 
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| lrMike Member Since: 26 Feb 2010 Location: Athens Posts: 177  
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Since the beginning of my driving life I always owned cars which never had any kind of external temperature sensor, not even as optional equipment. When I finally managed to fulfil my childhood’s dream and bought my beloved Defender back in 2010 I was hit by the no temp sensor curse for once more.
For several years I was happy enough to be informed by the scangauge but the readings were not accurate especially when my truck was stationary. For the few who are not aware, scangauge reads and displays the ECUs Air Intake Temperature measurement along the air induction line which means that when there is no adequate air flow, this temperature rises fast due to the proximity with the engine. Several days ago I thought it was time to come up with a neat solution that would cover the following requirements: 1) The temp display had to be as small as possible but with high visibility, day and night. 2) The placement of the display had to be somewhere that required no damage to the fascia. I follow the golden rule (at least for myself) that whatever change I make internally or externally must be reversible, should I ever decide to revert the car as delivered from the factory. 3) The price should be kept as low as possible. 4) Easy installation. Having all of the above in mind I decided to proceed with the following solution (total cost around 30 Euros): 1) Monochrome 0.96" 128x64 OLED graphic display installed on the right side (red arrow) of the part number FAG500420PUY as shown in the LRcat 
2) Waterproof DS18B20 Digital temperature sensor. 3) Arduino ProMini 5V as the main controller
4) 5V Buzzer for icy conditions alarm Kindly find below the installation steps: Preparing the plastic finisher for the display 1) Remove the two torx screws (lrcat pic numbered “4”) that hold the plastic instrument finisher in place. There is no need to remove anything else from the instrument panel and steering column area. 2) Now comes the only tricky part in the whole installation process which is to file down the plastic “nerves” in the backside of the finisher to create the necessary depth in order to seat the display PCB. This was done by careful use of a Dremel rotary tool. After you have a flat “deep” area for the display, next step is to open the actual rectangular opening for the display itself in order to be visible from the front. This can be done with a hobby knife or by careful use of the dremel. Special care must be taken to keep rpms low because the finisher’s plastic material is very soft and easily melts with the rotary tool. What we want to do in order to have a perfect finish is not to melt but to cut through the plastic. 3) Next step is to secure the display in place. All cables have to be soldered before this step, more details on the wiring below. I used glue bar from hot gun for securing and I covered the display’s PCB with insulating tape since the installed PCB will be very close to a torx screw holding the instrument cluster in place. Please find below a photo showing the installed display from the back side. Click image to enlarge 4) Although you can keep the display as it is, I chose to put a 3mm thick polycarbonate rectangle in order to cover the opening in front of the display and make it look flush with the finishing plastic. 5) In case something really BAD happened while trying to sculpture the whole plastic thing it is not the end of the world as this plastic part is easily replaceable and the original LR part only costs around 23 Euros. Caution!! For fathers having kids at ages between 2 and 6 like me, the described process must be done after they are put to sleep and triple checked that they are not going to wake up even after explosion. 
Wiring 1) To start, you'll need to solder the two jumpers on the back of the OLED. Both must be soldered 'closed' for communication with the microcontroller to work!
2) Connect the parts following the wiring diagram below: Click image to enlarge • The red cable going “UP” is the ignition live +12V supply and connected to pin RAW of the controller. The ignition live can be taken easily from the wiper lever plug. If I remember correctly is the green-white cable but better check with your multimeter. The black is GND and connected to GND. • The DS18B20 sensor comes prewired with black red and yellow cables as shown above. Red connected to VCC, black to GND and yellow to pin 9. • The 4,7k resistor is connected between the red (5V) and yellow (Data) pins of the sensor. • The + symbol of the buzzer is connected to pin 5 and the other pin to GND • For the display, GND goes to GND, Vin goes to VCC, Data to pin A4, Clk to pin A5, RST to pin 4. The rest are not connected. 3) Route the display cables behind the steering column down to the speaker. The microcontroller is tiny (33mm X 18mm) and can be installed in a small enclosure behind the speaker. 4) Route the buzzer cable in a place where it will be audible. The buzzer serves the icy road alarm. It is engaged after temp drops below 2 and beeps once for 3 times. 5) Choose a sensor location and route the cables. My preferred location was to route the cables down under the carpet and through the hole along with the plastic plug which holds the carpet to the aluminum floor panel then along the chassis to the inner side of the front bumper. An alternative and better solution is to route the sensor cable through the bulkhead but this required removing the instrument cluster. I chose not to do that for the 10th time during the last two weeks as before doing the temp sensor I finished the cruise control job which required a lot of playing with the area surrounding the instruments and the steering column. 6) Check all connections are secure without any short circuits. 7) Load the program through the optional FTDI programmer (more on this if there is interest from the forum members)  Pray…
9) Turn the ignition and look at maybe the most clear and beautiful miniature display you have ever seen. Click image to enlarge Click image to enlarge More on the OLED technology can be found here: https://en.wikipedia.org/wiki/OLED The most interesting part of this whole microcontroller game is that once you have one installed, you can add several other sensors like inclinometers, compass, altimeters etc. You can even add a GPS-GSM module for tracking purposes. The potential is huge, the prices are very low and the DIY electronics industry very fast evolving. Hope you enjoyed. 
Mike |
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15th Oct 2018 10:14pm |
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| Co1 Member Since: 19 Aug 2018 Location: North Yorkshire Posts: 3675  
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Great write up, thanks for sharing.
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16th Oct 2018 5:25am |
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| dgardel Member Since: 30 Nov 2008 Location: Veneto (Heart & Head) Posts: 3586 
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This is my solution
Before 2 DIN dash Click image to enlarge After 2 DIN dash Discovery 5 td6 HSE Stornoway Gray Outback Engineering Limited Edition
IID Pro MV License |
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16th Oct 2018 6:39am |
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| macfrank Member Since: 05 Nov 2015 Location: somewhere in the north Posts: 1076  
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Great job. Makes me want to dig out my Arduino stuff, which has been put aside in favour of a new time consuming hobby called "Defender"
For our camping use cases I would require a power connection to the aux battery, an additional internal temperature sensor and min/max temperatures for both with manual reset. So a very low power consuming software would be needed. |
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17th Oct 2018 12:37pm |
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| dotom Member Since: 04 Feb 2012 Location: Dortmund Posts: 90 
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Hi Mike, exactly what I’m looking for for a long time. Great job. Could you tell me / us please something about programming the controller?
Is there a special code necessary to show the temperature? Does it show a minus before the numbers when it’s below zero degrees? Best regards Tom |
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18th Oct 2018 3:04pm |
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| lrMike Member Since: 26 Feb 2010 Location: Athens Posts: 177
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The power requirement for this kind of applications is near zero. Something around the area of 100mA at 12v so no need to worry. |
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18th Oct 2018 6:09pm |
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| lrMike Member Since: 26 Feb 2010 Location: Athens Posts: 177
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Hi Tom,
The actual arduino code will be sent to you if you pm me. It consists of three main parts. The code for the display, the code for reading the sensor data and the code for the ice warning buzzer. It's a very simple code. For uploading to the board you will need an FTDI board like the one sold by sparkfun. Yes it shows a minus symbol for subzero temperatures. The resolution is 0.1 degrees and the sensor is digital which offers a lot of benefits compared to traditional thermistors. It is considered to be the most value for money temp sensor for non industrial uses. I can't wait to see this "seed" growing in other defenders here |
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18th Oct 2018 6:17pm |
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