TekPhobia

I'm using National's LM34 sensor. It's pretty accurate, and the voltage output is linear versus a logarithmic output of a thermistor. It's 10mV/F° which means .75V would = 75°F. The sensor can read temps up to 300°F but the accuracy starts to drop off. I certainly hope intercooler inlet/output temps don't exceed 300!!

-Tim

fastnikes

Very nice. I would love to see a finished product.
Have you thought about incorparating a EGT with it? is this even possible?

-Viet

TekPhobia

Anything's possible

For EGT, we would need a k-type thermocouple. The output is a voltage that is relatively proportional to temperature. In English....yea, we just need something to output a voltage in relation to temperature.

The current A/D chip I'm using is 4-channels. I'm only using 2 channels, so that's 2 free channels.

-Tim

hackish

The LM34's are a bit pricey but they are a nice sensor to work with... I used an atmel processor as it's got 8 - 10 bit ADC's. Getting a k type EGT is relatively simple - mostly software. I'm using a GM IAT sensor on mine. It's an EBC gauges and turbo timer all built into one.

-Michael

TekPhobia

Bah, they're only $1.99 at Jameco. If you want to be sneaky, you can order free samples from National Semiconductor. I suppose I could've used a different PIC with built-in A/D but all I have right now are 16F628's. Oh, I do have a 16F877 but that would be overkill for this project. I just wanted to avoid doing floating-point math -- which could be eliminated. But I like the 1:1 translation (e.g., 110 from ADC = 110°F).


-Tim

hackish

Ok, maybe I'm thinking of a different sensor - the one I was looking at was more like $15ea. FP math sucks but when you're running about 4 MIPS any old FP library will do. The initial prototype broke down costwise for me like this:
$5 atmel
$10 misc voltage reg, solenoid driver, resistors
$3 crystal
$10 board
$70 VFD

You can see how it adds up...

-Michael

91esibtuned

its worth the money

TekPhobia

My parts breakdown:

$3 - PIC
$5-10 for 5V switching regulator
$0 for passive parts.
$32 for VFD
$10 if I etch my own board

The VFD is the current hog so I can't use the standard 7805 as it is pretty inefficient compared to National's switching regulator which is 90% efficient. Talk about heat!

Speaking of efficiency, gas engines are only about 33% efficient: 1/3 is used for power, 1/3 goes out the exhaust and the other 1/3 gets absorbed into the block/water.

-Tim

fastnikes

Thats cool. If you decided to sell this it would be cool if you were able to do incorperate this. Then I would definitely be in the line of buyers. Keep up the great work.

-Viet