28022/ DS2760 thermocouple kit

barl

Hi,All,
I recently purchased 4 parallax thermocouple kits (part# 280222) that use the DS2760 thermocouple module, They are running on a BS2p to display cylinder head temp X2., oil temp and transmission temp. They work great and are accurate,
As far as I can tell parallax discontinued these a while back and I think I bought the last 4 available on the planet, I would like to purchase 2 more of these but no one has them in stock although they are listed on several web sights.
Does anyone know where and if these thermocouple kits or an equivalent item are available from
thanks,

Tracy Allen

You can purchase the newer DS2762 from Maxim-ic, and it looks like it would work in the same simple circuit. Mount it on a TSSOP16 carrier and add the two resistors and a capacitor that you can see on the Parallax 28022 data sheet.

An easy alternative is the MAX6675, thermocouple to digital interface chip. It is an soic8, easier to use with an SPI type inteface, and the cold junction compensation for type K couples is built in.

barl

Tracy, thanks for the reply,
the DS2762 appeard to use a thermoresistor selectable internal or external But a thermoresistor will not read temps. as high as I need, Was hopping to add exhaust gas temp. to my display, So that leaves us with the MAX6675 which would do the job But it requires 3 pins for communication im out of I/O pins on my BS2p , Im sure ther are ways to condense my I/Os with additional external components but its a lot more work and im running out of time, It really is dissapointing when you find the perfect product and they discontinue it,
Anyhow if you or anyone here of a 1=wire thermocouple interface even used i'm interested,
thanks,

Tracy Allen

That is not a "thermoresistor". The DS2762 and its ancestor the DS2760 were designed to monitor the health of Lithium battery power supplies. On either of those chips, the input in question simply measures voltage, but with a sensitivity sufficient to resolve microvolt-level signals. Normally, in a battery monitor, a resistor would be attached across those terminals and in series with the ground leg of the lithium battery, so the voltage across the resistor (shunt) is proportional to current. It is sensitive at the microvolt level so that the circuit can use a very small resistor. It works for thermocouples, but without the shunt. The thermocouple by itself produces a microvolt output at about the same level.

If you buy a DS2762 for this, don't get one that has an "025" suffix. That means that it has a 0.025Ω shunt built in, and you don't want that. The ones that don't have that suffix lack that, yes. It is a shunt though, not a thermoresistor. The application with thermocouples is off-book, a hack, butI don't see any reason why it would not work with the '2762. That is not to say it still might take small tweaks on the firmware.