LM35 temp sensor project

[jakeselectronics]

What do you recomend amplifying it with? Part no?

 

[dougy83]

Since your curious, ill give it a try tonight before fixing it . Ah, it means Vdd A? Since theres only 1 Vdd that means AVdd = Vdd?

AVdd is the analogue supply voltage. If it's to be the same as Vdd, it's usually a good idea to filter it with a RC (or other) to reduce the clocking noise fed into the ADC reference.

 

[dougy83]

Lm358?
Ts912?

 

[birdman0_o]

AVdd is the analogue supply voltage. If it's to be the same as Vdd, it's usually a good idea to filter it with a RC (or other) to reduce the clocking noise fed into the ADC reference.

Hmm, what kind of error would this produce?
Whats a typical cap value

 

[Mr RB]

I'd suggest amplifying the signal before feeding it into the ADC, and using a VREF >2V.

Yep, but there may not be a need to amplify it. Set the Vref for 2.048v resolution which will then be 2mV or 0.2'C resolution.

Then average 16 readings over a period of one mains cycle, so the few mV noise picked up by the mains is negated, BUT it also adds a +/- varying factor to the ADC volatge so when you average it you can get double the resoltuion with a fair degree of accuracy.

So you add 16 readings over a mains cycle, then divide the total by 8, (giving you double the resolution) so it is now at a resolution of 0.1'C.

 

[dougy83]

So you add 16 readings over a mains cycle, then divide the total by 8, (giving you double the resolution) so it is now at a resolution of 0.1'C.

Good point. Oversampling can be used to get a better resolution.

I read somewhere that you only need 4x sampling to get an increase of a bit (of course what you wrote is correct though). So if you have a mains cycle of sampling at 40kHz you can get 14bit resolution (using 10bit ADC)

 

[jakeselectronics]

So you add 16 readings over a mains cycle, then divide the total by 8, (giving you double the resolution) so it is now at a resolution of 0.1'C.

I can grasp that theory no problem. Great idea.
But when it comes to the actual program, whats the best way to divide a register by a value?

 

[dougy83]

Shift it right for every division by 2. e.g. shift right 3 times to divide by 8