Hi all,
I want to build a preliminary timer using 555 to get about 20minutes delay. Eventually I will go digital using a microprocessor after I have proved the philosophy of my control system works.
To achieve 20 minutes I will need a large value resistor and an electrolytic to get the time constant. But leakage through the electrolytic will upset the timer. To complicate it there will be about 10 cascaded timers giving an adjustable total delay of upto about 3 to 4 hours.
I tried measuring the leakage of a 47uF 16V tantalum cap but I can't measure it. I tried to measure the voltage across the 1M0 resistor in series with the cap and the 10V supply.
The resistance (10M) of my DMM upsets the voltage readings indicating that the effective leakage was a lot less than 1uA.
Q. is tantalum this good at 10volts? It appears to be a lot better than the data books state.
I want to build a preliminary timer using 555 to get about 20minutes delay. Eventually I will go digital using a microprocessor after I have proved the philosophy of my control system works.
To achieve 20 minutes I will need a large value resistor and an electrolytic to get the time constant. But leakage through the electrolytic will upset the timer. To complicate it there will be about 10 cascaded timers giving an adjustable total delay of upto about 3 to 4 hours.
I tried measuring the leakage of a 47uF 16V tantalum cap but I can't measure it. I tried to measure the voltage across the 1M0 resistor in series with the cap and the 10V supply.
The resistance (10M) of my DMM upsets the voltage readings indicating that the effective leakage was a lot less than 1uA.
Q. is tantalum this good at 10volts? It appears to be a lot better than the data books state.
Here's is another...
http://www.onsemi.com/pub/Collateral/MC14536B-D.PDF
There are a few more in the same (OLD) HV CMOS family...
These won't be so touchy over temperature.
http://www.onsemi.com/pub/Collateral/MC14536B-D.PDF
There are a few more in the same (OLD) HV CMOS family...
These won't be so touchy over temperature.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.