http://pcbheaven.com/wikipages/The_Schmitt_Trigger/
Non-symmetrical Schmitt Trigger using OP-Amp with single power supply
A variation of the previous circuit is the single power supply op-amp Schmitt trigger circuit. This circuit does not require positive and negative voltage for the op-amp to operate. The negative voltage of the op-amp is connected directly to the ground (0V) of the circuit. This is the schematic drawing:
The calculation of the two threshold points is different. To calculate the High Threshold Level, you solve the following formula:
RTOT = (R1 x RFB) / (R1 + RFB)
VTHRESHOLD_HIGH = V * R2 / (R2 + RTOT)
For the Low Threshold Level, you solve the following formula:
RTOT = (R2 x RFB) / (R2 + RFB)
VTHRESHOLD_HIGH = V x RTOT / (R1 + RTOT)
I have include a Non-Symmetrical Schmitt Trigger calculator using Op-Amp with single power supply in the Dr.Calculus page. Do not forget to visit and try it!
