Cherry alphanumeric display

Not sure I want to show off, but I have not seen anyone make anything out of one of these displays before, so I post in case anyone is interested.

The display is a 16 character 14+2 segment alphanumeric made by Cherry. They were used in some Williams and Data East pinball machines around 1989-1990.

The display is around 1 foot (305mm) long.

So far I have devised and etched a single sided PCB with the following:

DS3232 battery backed up I2C clock.
Slots for 4 I2C serial EEPROMs to store messages etc.
PIC 18F452 microcontroller
MAX1771 driven high voltage supply
CMOS 4514 BCD to 1 of 16 decoder
CMOS 4511 BCD to seven segment decoder

An interrupt routine runs at 960Hz, updating all 16 characters 60 times a second via the 1 of 16 decoder, for a flicker-free display. During the interrupt it also evaluates the ASCII characters to display and calculates the segments to be switched on.

The complete ASCII set has been predefined in a word sized array.

As an alternative, numbers can be sent via the BCD to 7 segment chip, although I am not currently using this.

This is all working well and I have now written all the routines for editing the clock parameters. It calculates the day of the week, leap years etc. Once written to the DS3232 they can, of course, be read back in.

Now this is all working, I can concentrate on the fun stuff, which is scrolling some messages and generally making the whole thing much more chatty.

That's some nice work. I'd love to publish a feature of this project on Hackaday.com but it needs just a little more info.

Any chance you'd be willing to post some of the following: picture of the back of the board, a schematic, code, video if you have it?

Well I lied, I just measured it and it is 11 1/2 inches long.

These displays are fast drying up, but you can still buy them new from around 100 US dollars upwards, plus shipping.

See an example for sale here.



They are cute displays. The original boards mostly suffer from the UDN high and low drivers being driven close to their their max ratings, so the boards in pinball machines are often problematic, especially 20 years on.

The UDN chips are hard to find now and so I rolled my own drivers, which include a pull mid to minimise ghosting.

LED replacement boards for pinball machines are now available and I happen to have four good glass envelopes that were discarded after LEDs were fitted. Displays are fitted in pairs, so there's often a good one going spare if you know the right person.

szczys wrote:

That's some nice work. I'd love to publish a feature of this project on Hackaday.com but it needs just a little more info.

Any chance you'd be willing to post some of the following: picture of the back of the board, a schematic, code, video if you have it?

Yes I'll write the project up, take videos etc, when I have finished the code, which I am about half the way through. It's working fine as a clock, but I want to do some fancy scrolling and stuff like that.

I had some horrendous issues with the high voltage section - fast high voltage spikes getting into the feedback path of the voltage regulator. Seems OK now, after I re-routed a few components.

I don't have a schematic, but I did do one for the segment and digit drivers. I went straight to an iron-on PCB.

The board is not so pretty after I butchered it here and there trying to fix what I thought might be earth loops. I changed a couple of things to isolate the high voltage earth away from the digital stuff.

Its been a steep learning curve for me, I hit all kinds of issues, mostly trivial once I worked out what was happening.

I have to make three more of these, so my next board layout will be somewhat neater as a result of what I've learned.

Here is a picture of the back. You can see the MMBTA42 and MMBTA92 drivers and the DS3232 clock. Not a pretty sight, all things considered, but very steam punk.

The first thing I did was to mount the glass display onto a fat slab of acrylic so that I didn't break the nipple off the back. I'd hate to do that.