I recently acquired (free!) an obsolete frequency counter which uses a Nixie Tube display. I don't really have much need for a counter, so I decided that I would rip out the tubes and any other possible circuitry and make myself one killer desk clock. I now have read a ton on both Nixies and digital clocks, in preparation.
I was thinking to build the clock using basic decade counters with a crystal oscillator divided down to 1Hz- I have that part of the circuit pretty much figured out.
The Nixies require ≈200vdc to run. I was thinking that a voltage doubler from mains current would be the easiest way to get there- however I have no experience with them. Does anyone have any ideas for appropriate capacitor values? Any equations I can use? Current draw will never exceed 100mA, with 25mA typical. I can accept up to 25V ripple.
My other question is about using about supercapacitor backup for the timekeeping circuit, so I don't have to reset every time AC is lost. 1 Farad supercapacitors are actually pretty cheap, and I never want to have to replace a battery. I'm looking at powering about 10 CMOS chips at less than 1Hz, plus a few LEDs.
Does this power supply circuit make sense?
(in case you can't see, that's a 10microFarad filter cap.)
The notion is that when the power is on, the top PNP transistor stays off, the 1F cap charges, and everything goes happily. When the AC power goes off, the top transistor polls low, causing the LED to light as an indicator that the circuit is on backup. It also causes the bottom transistor to turn nonconductive, locking the ground rail and preventing the cap from just draining through the rectifier.
Thoughts?
I was thinking to build the clock using basic decade counters with a crystal oscillator divided down to 1Hz- I have that part of the circuit pretty much figured out.
The Nixies require ≈200vdc to run. I was thinking that a voltage doubler from mains current would be the easiest way to get there- however I have no experience with them. Does anyone have any ideas for appropriate capacitor values? Any equations I can use? Current draw will never exceed 100mA, with 25mA typical. I can accept up to 25V ripple.
My other question is about using about supercapacitor backup for the timekeeping circuit, so I don't have to reset every time AC is lost. 1 Farad supercapacitors are actually pretty cheap, and I never want to have to replace a battery. I'm looking at powering about 10 CMOS chips at less than 1Hz, plus a few LEDs.
Does this power supply circuit make sense?
(in case you can't see, that's a 10microFarad filter cap.)
The notion is that when the power is on, the top PNP transistor stays off, the 1F cap charges, and everything goes happily. When the AC power goes off, the top transistor polls low, causing the LED to light as an indicator that the circuit is on backup. It also causes the bottom transistor to turn nonconductive, locking the ground rail and preventing the cap from just draining through the rectifier.
Thoughts?