Glad you got it to work, you could remove D1,D2,R2, and just have R1 connected from pin3,

But who cares its working well done.!

 

The green wave is between the control pin on the 555 timer (pin5) and the .01uF capacitor, C1 on the diagram I posted before. The yellow wave is at the output pin (pin 3) on the 555 timer or between R1 and R2 on the diagram.

 

I got it working! I used the LT 1635, checked the pinouts, talked with the electrical engineering professor who recommended the part, plugged it in with the same resistor values and voila! Maintained 33.1 degrees Celsius all night, and super fast response from the thermistor if I spray it with key board air can or hit it with a heat gun. Super happy!

One last question and comment on this. It seems to have a fair amount of noise as you can see from the next picture. It doesn't seem to really effect the performance but if it's an easy fix, I would like to fix it. But I'm also of the mindset that if it aint broke, don't fix it. It seems to change when I move the power leads to the peltier and also when I move the leads for the thermistor. Should I wrap wires with something and ground them? Or should I not worry about it since it does work.



Lastly I just wanted to thank everyone that has responded to my questions and made suggestions. This was my first time posting in this forum and it was nice to not get condescending, belittling comments. I have seen that a lot in other forums with people who are not well educated or informed on what they are asking about, and it was nice to just get knowledgeable well-informed answers.

It's quite possible that when the output switches that noise gets picked up on the thermal-couple. You could shield the line from the thermal-couple, or you might try a .1ufd in parallel with R11. This will make the op amp less responsive to high frequency noise.
It would also be a good idea to add some decoupling capacitors from the 5 volts to ground. A big cap on the 555 and perhaps a smaller one where the line goes out to the thermal-couple.

 

Where on the 555 should I add the big capacitor? between pin7 (V+) and ground?

 

Where on the 555 should I add the big capacitor? between pin7 (V+) and ground?

Yes.

 

Excellent suggestion went ahead and tried that and ended up with this:


I didn't try decoupling capacitors because honestly I don't even know what they are or where they would go. That looks good enough to me!

 

Decoupling caps are also known as bypass capacitors. They set very close to the IC power pins. A usual value is 0.1 uf ceramic unless the manufacturer suggests otherwise.

They can be a parallel combination of different types of capacitors.

 

Excellent suggestion went ahead and tried that and ended up with this:


I didn't try decoupling capacitors because honestly I don't even know what they are or where they would go. That looks good enough to me!

I'm guessing you added the cap in parallel with the resistor?????
Decoupling caps are just ordinary capacitors across the power supply. The 555 is known for it's noise generation when it switches. But that does look much better.
Is the green trace the control voltage at the 555?

 

The green trace is the opamp output to pin 5.

That's what I thought as well. Still a little noisy considering it has a .01 and 1k feeding it. Now I'm wondering about the other trace only being 1/2 volt.

 

Yeah I added the capacitor in parallel with the 1k resistor, it's a .1uF capacitor though not a .01. I also added a large 33uF capacitor on the V+ pin for the timer. Maybe I misspoke earlier but the green wave is not pin5 on the 555. The green wave is pin6 or threshold on the 555 which also has a .1uF to ground.

Do you see any problems with this, the way its set up now? I do plan on shielding the wires once I design and mill a board for it, which I'm confident will reduce the noise.

 

Yeah I added the capacitor in parallel with the 1k resistor, it's a .1uF capacitor though not a .01. I also added a large 33uF capacitor on the V+ pin for the timer. Maybe I misspoke earlier but the green wave is not pin5 on the 555. The green wave is pin6 or threshold on the 555 which also has a .1uF to ground.

Do you see any problems with this, the way its set up now? I do plan on shielding the wires once I design and mill a board for it, which I'm confident will reduce the noise.

Looks like your ready to go. Matbe you could put it in the fridge and make sure the temperature holds, but I think it should.