Parts List:
| Part |
Description |
Radio Shack # |
DigiKey # |
Notes |
| R1 |
1K resistor |
|
|
brown black red gold |
| R2 |
1K, NTC |
|
|
|
| R3 |
10K resistor |
|
|
black brown orange gold |
| P1 |
10K trim pot |
|
|
bourns, multi-turn |
| D1 |
Led, red |
|
|
Light Emitting Diode |
| D2 |
1N4148 diode |
276-1101 |
1N4148DICT-ND |
Signal Diode |
| Q1 |
BC547B, transistor |
|
|
General purpose, NPN |
| Q2 |
BC547B, transistor |
|
|
General purpose, NPN |
Couple Notes:
The R2 thermistor is a regular NTC (Negative Temperature Coeficient) of about 1000 ohms. But other types will work
too. Adjust the sensitivity with the 10K trim-pot P1.
When the thermistor is at operating temperature, the resistance is high.
The phone number for DigiKey is 1-800-Digi-Key.
Copyright:
The original circuit was published in the Dutch "Elektuur Magazine" in 1999.
The modified circuit above is © Copyright 1996, Tony van Roon.
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Copyright ©2003 - Tony van Roon