- ... If I used an existing microcontroller that was - programmed for a seven segment LED clock would the same - firmware work for driving the 7 segment VFD tubes or are - there timing issues that would be a problem? ... - Robert W8UUU
Should still work. A couple of things to look out for: (1) Voltage, obviously. But, also dependent if the clock is multiplexed or static (direct drive). 50V-60V, if multiplexed. 20V-30V, if static. (2) For LEDs, the anodes, and cathodes are of opposite polarity. To turn ON and LED, the anode is made positive (+), and the cathode is made negative (or more negative, usually gnd). In a VFD, the anodes are still the anodes, so that stays the same (other than See 1). BUT, the grid is also made positive (NOT negative). So you'll have to invert the signals coming out of the cathode driving outputs. If there are external drivers, then you need to look if they invert also. Sometimes there's a double invert; to get a non-inverting drive. The 'rookie' way to adapt this would be to use a 3rd layer of inverters, such as 7404s or 4069s. Another way is to use a transistor in 'common base' hookup. Tie the emitter to the uC output pin. Tie the base to some positive voltage, somewhere between the uC positive supply, but at leat 1V above gnd. The collector still is connected to the VFD, with a pull-up resistor. 'Common Base' is non-inverting; 'common emitter' IS inverting. Or use a negative VFD supply (-60V), and drive it like an example in my skydrive: https://skydrive.live.com/?cid=f9db37b8211ce831 Look at the 'Snippets' folder, and look for files starting with VFD. VFDs draw current, in the positive direction. If a negative supply is used, then active components (transistors) will be doing the heavy lifting. Otherwise that would be left to resistors, which would have to be made smaller, and waste power. (3) The cathode/filament should stay static. That is, not involved in multiplexed timing. If the filament voltage is relatively high (over 3V), then AC should be considered to avoid a brightness gradient. Also the average DC bias of the cathodes, should be a little more positive (5V), than the maximum negative swing, of the grids. That way the grids will look slightly negative, when OFF. Timing should not be an issue. VFDs having a vacuum, and being somewhat small, should have response times similar to LEDs. Both of which should be able to be switched in the low MHz. That's a lot faster than any multiplexing you'll be doing. -- You received this message because you are subscribed to the Google Groups "neonixie-l" group. To post to this group, send an email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/neonixie-l?hl=en-GB.
