'lil Project

[Vimmy]

Hi Guys, I have been working on a wee project in my shack, with time allowing and a temperature above 6 degrees, to set up a system to monitor air temps either around the engine bay or inside air intakes etc.

The most basic system uses a standard K-type thermocouple connected to a chip that reads the low output voltages (0.049mV) per degree centigrade and convert them to a more respectable value of 10mV/Deg C. This then is fed into a mini voltmeter/lcd display which then converts every 10mv/Deg C. to a 1 on the counter/display device so that it reads directly any temperature measured by the thermocouple.

I've not done any proper design/electronics for a few years and have got the bug again, so much so that I've extended the device to read off of up to (so far) 4 different thermocouples to watch different temps at various points in the engine bay/air intake system using remotely switch relays. I have other plans to have the relays, when switched in, to show on another display which sensor number is being measured. The current method is using a cumbersome 4 way switch which is going to be hard to mount in the car without looking 'fugly'.

I have some parts on order to put together brass compression glands so that these thermocouples can be put into the intercooler pipe work (for example) to measure the air intake temps at different stages. The whole idea came about as I couldn't justify spending lots of money on 'branded' devices and displays and wanted to watch what the car was doing with its age and mileage ever increasing. It was also designed to be easily repeatable and be used from off-the-shelf easy to find parts which did not cost the earth.

If anyone wants a copy of the diag's to build their own, I can post it up, it still in the experimental 'Heath-Robinson' stage and not a 'production' version as yet but not far off. The last thing had in mind with this project was for it not to turn into a 'fast n furious' system with under car lights et al, but thats given me another idea.......

Cheers,

Col

[stum450n]

Sounds great! Just one thing though...

[Vimmy]

Ah yes, its a secret patented design, the pics are there really, you just have to find 'em

[mark1234]

i'd be interested in that

[Big 'D']

i'd be interested in that

Me too

Cheers Iain

[Vimmy]

Ok chaps another few hours trying to document the build so far. the piccy below (24bit bmp taken from Visio) may look a bit fuzzy but I can mail you the better quality version direct if you wish. This shows a basic/single thermocouple kit connected to the (interface/compensating amplifier) AD595 chip and then onto the Anders OEM335A module which then displays the output temp with 1 decimal point ie 10.1 / 56.3 etc etc

[Vimmy]

Ok this one shows multiple thermocouples being switched via relays which are controlled via a 4 way switch. I want to expand the switch idea to use IC's instead with an up and down set of buttons/switches which then control a counter to give an unlimited amount of switchable inputs (based on the similar number of relays).

With this up/down switch idea I want to add a small alphanumeric led display to show which numbered sensor is in use but this is still being designed and tested at the moment. The switch hasn't been implemented as yet as I'd prefer the IC route as its not far off and is shown just for clarity.

I will get some pics tomorrow when the shack has defrosted a bit to show the small size of the boxes used to house the differing modules. This can all fit in a bigger box, depending on application, the sky is the limit really

.

Multiple.bmp

[Vimmy]

To try and remove a bit of confusion with the previous diagrams see attached which shows the Logic switching and signal boards to make some sense

[Vimmy]

Ok last diagram, this shows the manual switching config required to switch in the relays, the power supply and the display board. Hopefully this is clear enough , if not I can send out Visio diagrams.

If anyone wants a hand building and testing some of this stuff, I can help anytime. The only part I wont be much help is the final finishing of box displays etc as I have about as much artistic vision as a banana, sorry to all the bananas out there that my read this

There's a bit more to come with the logic/IC/counter design as its very much dependent on the number of thermocouples you want to switch in.

I was looking to use this kit as a whole for other temperature readings for example brake temps, but is would need a thermocouple to have some form of attachment which I haven't looked deeply into yet. It could also be used for EGT probes too, all that is required is a different attenuator rating before it goes into the display module, again dependent on the output characteristics of the high temp thermocouple in use.

[mark1234]

are these all chips or do you have to make each individual circuit?

[Vimmy]

Hi Mark, the AD595 amp is a dedicated chip and the OEM335A is a dedicated chip also but houses the 4 digit display on the back of it.

AD595 Datasheet Linkie

OEM335 Datasheet linkie

The other components are small discreet devices which can be mounted on a small section of Veroboard, as mine is. I didn't bother with building a dedicated pcb as its pretty straightforward to construct

If you only want to run a single thermocouple into the display you will need to connect the following:

1. Two wire Ktype thermocouple to pins 1 and 14 of the AD595, give it a +5v feed

2. Send the AD595 output via another pair of wires (ie pins 8/9 Signal and pin 7 ground) to pins 3 and 4 of the OEM335 chip.

3. Using the OEM335 datasheet, there is a DC Voltmeter example that uses a resistor divider to reduce the input voltages.

At the moment the input to the display changes 10mV for every degree change in temperature, so the display would show a 10 rather than 1, so I used a 10:1 divider to reduce the input voltage and hence the display reads correctly. This also means that the temp display possibly now read up to 200 degrees or higher with a resistive divider change and a different thermocouple to match the higher temps

I can bring round the hopefully finished kit after christmas if you want to take a look. My version is built using small ABS boxes as I was using these for other projects in the car and things have progressed from there, but it may be easier to house it all in one perhaps?

Cheers,

Col