'Project' Temperature Circuit Help

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kbyrne

Joined Dec 10, 2011
92
I have a few questions on a LM35 and LM3914N temperature circuit that I need assistance finishing. Circuit is powered by 7VDC. It has 3mm LED"S and 20 of them. How do I figure out the adjustment part of the circuit?
1 Trim R-3 for 3.074V @ Leg # 8 IC. #2
2 Trim R-2 for 1.055V @ Leg # 4 IC. #1
3 Trim R-1 for Pin #5 both IC'S 0.075V +or- 100mv/ degrees celcius
@ T ambient.
I am new to electronics and cannot get a different voltage reading with adjustments to R2 or R3. Could the reason be Carbon film resistors @ 5% instead of 1% resistors. Can that degree of change on schematic cause that problem or where else do I look. Voltage to both IC'S check out and LED'S light in a row about half. Thankyou.:eek:
LM35 TO-92 Left side of gif then R1, R2, And finally R3.
 

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wayneh

Joined Sep 9, 2010
16,102
I am new to electronics and cannot get a different voltage reading with adjustments to R2 or R3.
Are you saying that the voltage stays fixed regardless of the position of the variable resistor? What are you actually observing? A cheap pot might make adjustment difficult, but should certainly change the voltage.

A photo of your build would be helpful also. Indicate where you are measuring your voltages.
 
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