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It looks like I'm good on the input range, now to figure out the output range. The 358 is "designed to operate from a single power supply and it's common mode input range includes ground". It does not say rail-to-rail. I was thinking this may be a good fit for the circuit where I'm really only using the lower three-quarters of the voltage range.
The datasheet is here https://www.electro-tech-online.com/custompdfs/2012/01/lm358-n.pdf
I think the purpose or function has been somewhat lost. I need to detect ice, or ice being present.
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I think the purpose or function has been somewhat lost. I need to detect ice, or ice being present. When the sensor is in free air, I expect it to be near room temperature.
Any thoughts on the selection of the LM358 op amp?
Did you see my prely earlier? Rather than detect ice, you could just ensure ice does not occur. By putting the sensor on the coil, and keep ing the coil just above freezing point you will still get the maximum possible cooling effect from the same hardware but ice will never form.
Actually the overall performance should be higher as ice is an insulator, and a system that never ices should get a better overall heat transfer from coil to the air.
The purpose/function has not been lost, you dont want to detect Ice, you want to know when the LM34 output is at or below 820mV and the output is at or above 900mV.
I know what this means, but why do you think it wouldn't be.??
When the sensor is in free air, I expect it to be near room temperature.
Any thoughts on the selection of the LM358 op amp?
As explained the LM358 output will not go higher than Vsupply-1.5V, so for a 5V supply thats a maximum of +3.5V.
The dual supply idea will not make any difference to this +3.5V level.
That changes things a bit. I (obviously) misread the LM34D d/s. Instead of trying to detect 32 degF at 320mV and 72 degF at 720mV, I'll be looking at 0V and 400mV. So I'm definately going to want that 5x gain.
Can you help me understand how the d/s output spec relates to no outputing higher than Vs-1.5? The clip you provided looks like Vs-4.0 worst case and Vs-2.0 typical. Am I correct in understand that the input cannot exceed Vs-1.5.
I'm looking at the D version, 32 to 212 degF.
I'm looking at the D version, 32 to 212 degF. I guess the comment "Definately going to want the 5x gain" was being over zealous. More appropriately I should have said "I can definately use the 5x gain".
Interesting App note. What does CM Vi stand for?
Look at this clip from the LM34D d/s.
The minimum expected tempr is +3F using Fig #1 on Page 2 of the d/s,,, look at Fig #2 as an option.
I see that now. Single supply will not get below 3-5 DegF output. Bummer. I'd really like to avoid dual supplies. I'll have to think on it a while, but the 3-5 degF limitation may not be a problem (but it would be better if it did read to 32F instead of 35F). If I set the thresholds for 50-55 degF not reading to 32 won't be a problem.
We're obviously passing each other in posts.
The output will be 40degF=400mV instead of 80mV ([40-32] *10) as we thought earlier.
Based on your d/s clip fo the LM34, the D may not be accurate below 3-5degF? Or it won't read below 3-5degF?
In the LM358 app note, I saw the CM Vi parameter first. I now see the Vo parameter further down. Vo max =Vs-1.5. With Vs=12V that shouldn't be a problem.
The 3F minimum on the LM34D means an absolute minimum V of~ +30mV, which in Centigrade is -16Cdeg. I would say your application will never get that cold, I hope.!!
Can you update me on how you plan to use the 'amplified' of say 5Vmax.??
I don't want to cycle the dehumidifier that often. It takes only minutes to tens of minutes for the coil to reach freezing. Any temperature below the dew point is effective at dehumdification. But too much ice build up blocks off and restricts the air flow. So some ice build up is OK. Too much is a problem.