Original question:
On the suggested schematic, i would like to change the RC network so i can have a 1Hz pulse with 10-20msec duration.
I don't know how to calculate the resistor/capacitor values.. can you help me please?
Hi Christos,
if the duty cycle is far away from 50%, I would use the double feedback technique, using one feedback path for the high time and the other for the low time:
When filtering the supply voltages powering the OPAmp and the voltage divider R3 / R4 and when using high quality foil capacitors for C1 and C2, the circuit will be surprisingly precise.
I have used high ohmic feedback resistors to save supply current. R6 is needed to limit the input current.
The output signal can also be inverted by reversing the diode. But the circuit will draw much more supply current then:
I certainly need not to mention that such a high ohmic circuit needs good shielding against hum and interference.
Kai
The correct value of R1 depends on the actual capacitance of C1. As capacitances usually show huge production tolerances, you might want to select one cap with low tolerance from a handful of caps. After that adjust R1 until the period time is exactly 1s.
Don't decrease R3. As the output voltage of TLV7031 cannot fully go down to 0V, this would make it harder and harder for the comparator to toggle.
Kai
Thank you kai klaas69
I might need to order new pcbs after all...
I made the ones i have now according to this and it does work nicely but i cannot adjust the component values to have the output 980-990ms OFF 10-20ms ON
