Need help locating a component

[kf4sqb]

OK, so this isn't really Motorola related, but I haven't been able to find what I need, and I'm hoping someone here can help. I'm trying to find an IC to convert binary (at least 5 bit) to BCD, or to take a binary (at least 5 bit) input, and drive a 14-segment LED display. So far, I've been able to find one part number, DM74185 (a datasheet can be found here), but I can't find a source for it, unless I want to buy in bulk, and I don't need but one. Can anyone here help me out with this IC, or something similiar?

PS, mods, please (pretty please?) at least let this stay a few days before locking it as off topic. I really need a hand here.

[Al]

I built something very similar to what you speak of quite a few years ago when I needed to take binary from a Datex shaft angle encoder and drive seven segment displays(if I remember correctly there were 5 seven segment indicators in the whole display). As I recall, I needed to burn some small proms(fusible link) to convert the BCD to the format required to drive the displays. I may still have some of both ICs left, I'll check if you wish.

[jackhackett]

If all else fails, and you have access to a E/EE/PROM programmer you can make your own decoder (that's what that chip is based on, a PROM).

The 8 data lines on the PROM would be divided into two 4 wire BCD outputs, then the 5 binary inputs would go to the lowest 5 address lines with the others tied low. For each binary input the PROM would be programmed to put the proper BCD outputs on the data lines.

That would get you BCD, if I knew exactly what kind of display you're planning to use (multiplexed? common anode or cathode?) I might be able to come up with something better.

[kf4sqb]

Ahh, the power of the Batboard! That's more info than I expected, sooner than I expected. I've seen some info on the web about using a PIC microcontroller to do this, but nothing about using a plain old PROM. That will certainly be possible, as I have a burner, and even a few old PROMs laying around. Jack, would I be able to use a 28 series device, like a 2816, 2864, etc? I have a few old 27 series laying around, but I don't (yet) have an eraser to blank them. As for what type of display, it will be common anode, since I have one laying around. I certainly have no idea how to write up a "codeplug" to burn into the PROM. Thanks for the help, guys!

[jackhackett]

Is the display a multiplexed type? Two digits with the segments of each tied together into one set of a-f pins?

[kf4sqb]

No, just a pair of plain 7-segment displays.

[jackhackett]

I forgot to say earlier, a 2816 should work fine.

Okay, I think the easiest way to do it then would be to program the prom for two 4 bit BCD outputs, Data lines 0-3 would be the low digit, 4-7 the high digit. Those outputs would go to a pair of BCD to 7 segment decoders (7447, commonly available) which would drive the displays. http://www.hcc.hawaii.edu/~richardi/113 ... _4/2f4.htm

As for the prom programming, what you basically need to do is use the 5 bit binary number you want to decode as the address, and put the BCD equivalent in each memory slot. Since the BCD numbers for 0-9 are the same as for 4 bit hex, the hex numbers you program into each address would be the number you want displayed:

addr --- data
binary - hex
00000 - 00
00001 - 01
00010 - 02
00011 - 03
00100 - 04
etc. up to 31

just start at address 0 and fill in the numbers 00 to 31 for the hex data, simple.

I'm pretty sure that's right, but it's late and I'm tired so someone might want to double check it, lol.

[kf4sqb]

Jack, is it really that simple? If you don't mind, give me an email addy, and I'll send you a .bin file to look over and see if I did it right. Thanks!