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Lloyd's Model E340 Series 255A Answered

Look at this old calculator I bought for like $2 at a church sale. I just got around to taking it apart and it looks like a Nixie tube for the display, whatever it is, it's definatly sealed glass. I can't get any pics of it powered up srry because some dumb fart must have left dead batteries in there, I couldn't figure out why it wouldn't work with fresh batteries. Well I figured out, look at the pictures, someone never cleaned the battery acid out of the inside and it ate away at some of the PCB So I wanna know, can I like hook this tube/display up to my computer through the serial port or something?? It's got 9 digits. Sorry for the sh*t pictures :(


This type of display is a VFD (Vacuum Flurecent  Display) NIXIE tubes are gas discharge tubes. They both use voltages that are much higher than in a PC so driving them requires drivers.


 How would you recommend driving them?

These are actually forms of traditional vacuum tubes. There is a filament (heater) which also doubles as a cathode. This needs a small current to just slightly heat the wire. This is normally a few volts at a few milliamps, but on a long tube this will usually be AC. If too much current flows the wire will glow and the tube will be destroyed. Next there is a grid this turns on and off each digit. A positive voltage on this will turn on the digit. A negative voltage will turn off the digit (not driven also works). Finally each of the segments are anodes, these are driven to a higher voltage (25-60VDC). The electrons will cause the digits to glow. To drive this you need level shifters to change the 5V logic on a PC to the higher 25-60V . Maxim makes one of these parts: MAX6921. You also need some software to quicky display each of the digits so that with POV it looks like all of the digits are on at the same time. If the calculator is old enough there may be a seperate inverter (converts 9V to 25-60V) and driver chips and then the calculator chip.

Nice find! I have two of those ti-55s with the led displays.

sigh..that's a shame that no one even cares to look at my topic posts anymore.