Anti-Freeze (Detector)
I present a circuit from an older electronic magazine, but maybe quite popular for some older people.
Attached to a car, in the vicinity of storage systems or warehouses, agricultural farms or animal husbandry, a device to signal the danger of frost is always welcome.
The presented scheme uses as probe a NTC thermistor (TH1) of 10kohm and as warning elements three LEDs: green for temperatures above 3..4 * C, yellow for 1 ... 2 * C when there is a possibility of frost and red for signaling 0 * C and below. The control functions are performed by two UA747 comparators, with hysteresis. The semi-adjustable RV1 and RV2 are used to adjust the 3 thresholds, signaling the LEDs connected to the 2-3-15 outputs of the CD4028 (U2). Below 2 * C, RV2 is adjusted so that output 2 of U2 (yellow LED) is active, and below 0 * C the same setting is made for RV1. A 12V power supply would be needed.
BOM:
"C1" "100nF"
"C2" "100nF"
"C3" "10uF"
"C4" "10uF"
"C5" "100uF"
"D1" "Red"
"D2" "Yellow"
"D3" "Green"
"D4" "10V"
"D5" "1N4007"
"J1" "12V"
"Q1" "2N3904"
"R1" "33k"
"R2" "3k3"
"R3" "3k3"
"R4" "1M"
"R5" "3k3"
"R6" "3k3"
"R7" "1M"
"R8" "220"
"R9" "330"
"RV1" "22k"
"RV2" "22k"
"TH1" "10k_NTC"
"U1" "UA747"
"U2" "4028
P.S. I'm not the original author of this circuit, I just drew it.
Anti-Freeze (Detector)
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