Hi Prashant, > I've just obtained a few vacuum fluorescent displays(VFDs) from a surplus > dealer and am looking at interfacing them to the PIC. The part no. is > Futaba 4-LT-105Z. It is a timer(88:88) display which seems to have been > made for an oven. What's the best way of driving them from a PIC 16C84? > I haven't used VFDs for a while now and any pointers to resources on VFDs > in general would be great. You will have a fillament that will draw significant current 40 .. 120 mA would be a likely figure. The fillament is at the lowest potential, preferably the midpoint is at ground and the two ends have an AC drive voltage byt this is not common these days as it would mean an extra transformer winding. So instead one puts one end to ground and the other end to a DC voltage 2 .. 6 V typically either positive or negative. The fillaments should heat up enough to just be visible in total darkness with no other signals present. They take about 1 .. 3 seconds to heat and about 0.5 seconds to burn out if you over voltage them too much. The drive is now referenced to the 'ground' potential and consists of similar segment and digit drivers. They are made to work at 0 .. 12V positive these days while in the past the voltages were higher. You need to have some form of intensity balancing in long displays if you have a DC fillament voltage as the drive voltage varies from 12V at one end to 7V at the other end and this can be achieved in two ways at least. One is to have the digit grids driven through a resistor of magnitude such that the digit intensities are all the same as the dimmest digit at the lowest voltage end of the filament. Once you drive the display with a PIC you have another option and that is to duty cycle modulate the digit on times, make the dimmest digit selected for longer. The relationship should be close to linear across the display. The drive of the segments is set the segments you want lit ti 12V and then set the digit grid to 12V for the digit in question with the other digit and segment lines at 0V. Refresh at faster than the visible flicker rate, the phosphor supplies extra persistence so you can probably get away with anything over 10 Hz but 30 Hz will be flicker free. The drivers on a Futaba type LT display I have are NE594 and have 8 High side drivers with TTL inputs. With your 5 digit display you would need 5 + 8 drivers if you want to use the decimal points and the colon, just the numbers would need 4 + 7 so you will need 2 ICs 8 or 7 drivers per IC would be enough. You could suffer the high side drivers with 2 transistors each but a lot more work. Beacuse of the persistance you can also go do other things for a short while in the PIC code without flickering of the display. Cheers -- Kalle Pihlajasaari kalle@ip.co.za http://www.ip.co.za/ip Interface Products P O Box 15775, DOORNFONTEIN, 2028, South Africa + 27 (11) 402-7750 Fax: 402-7751 http://www.ip.co.za/people/kalle DonTronics, Silicon Studio and Wirz Electronics uP Product Dealer