MAX1496 ADC LED Driver

Hi, I'm building a digital temperature gauge. I purchased this kit from Jaycar a temperature switch with LCD readout **broken link removed**
There were no problems with assembling the kit as such, and it seems to work fine. The issue is that the supplied LCD is quite large and it is not backlit so it is not suitable for use in my car. I tried searching for alternative LED displays but they all seem to be overly large, or unsuitable for use with the kit.
So, I started looking at ADC's and LED segment drivers and found the MAX1496, an ADC with 3.5digit LED driver in one package.

The Jaycar kit uses a 0.1mV/degC signal to drive the original LCD. I changed some resistor values to increase amplification of the signal to 1mV/degC to better suit the MAX1496. The Jaycar kit also has a 5V power supply onboard which can drive the MAX1496.

I've assembled the MAX1496 on an experimental PC board, and it seems to work to an extent but it is having some issues.
I just wanted to clarify what is explained in the MAX1496 datasheet. If you go to page 9 on the datasheet it has pin descriptions.
How do I know if I want to use internal reference or external reference? Also, alot of the pin descriptions say bypass using a cap to ground. Does that mean the pin is connected to for example the analogue input and also to ground via a cap?

I have schematics of the Jaycar kit and of how I assembled the MAX1496 board. I can scan these in if you need them.

Thanks, Luke

hi,
I expect you have used the circuit on page 20 of the datasheet.?

Some of the functions of the ic will not be used in your application.

A bypass with a capacitor to ground means connect a low value cap say 0.01uF from the specified pin to 0V.

Does the circuit you have built work OK on your prototype board.?

Yeah the circuit shown on page 20 is pretty much what I simulated on the prototype board. I understand that some functions may not be used such as internal reference, but I'm not sure if I should be using it or not.
The circuit I've built has issues with stability and giving false readings, I suspect this would be due to my lack of installing bypass capacitors. I'll get them on the prototype board and see how it goes.

lukiss99 said:

Yeah the circuit shown on page 20 is pretty much what I simulated on the prototype board. I understand that some functions may not be used such as internal reference, but I'm not sure if I should be using it or not.
The circuit I've built has issues with stability and giving false readings, I suspect this would be due to my lack of installing bypass capacitors. I'll get them on the prototype board and see how it goes.

Click to expand...

hi,
Always use power supply decoupling capacitors on your logic circuits.

That is 220uF at 25V [for a car battery psu] and a 0.1uF capacitor from the logic +V supply to the supply 0V, as close as possible to the MAX ic.

How 'clean' [ any electrical interference] is the analog input voltage from the sensor.? An oscilloscope would be useful to check the sensor to MAX voltage.

I'll go over again and install the appropriate decoupling/bypass capacitors and see how it goes. Unfortunately I was put to work in a different area today and won't have access to my project for a few weeks (I was doing it at work in my spare time).
I'll update when I make some progress. Thanks for your input.