Jellybean barcode driver part?

Is there such a thing as a jellybean 74- or 4000-series part that takes a binary or BCD input and drives a bar graph LED from it?

I need to drive an 8-LED bar graph from a 4-bit data source with the minimum of components, and right now the simplest option appears to be a micro (well, or a PAL, but it's easier for me to develop a micro).

The drive lines are output-only and can't be switched very quickly, so that rules out putting an I2C or SPI I/O expander on them.

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larwe
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In article , larwe writes

Two 74ACT138's would do it if you are happy to have "spot" mode rather than "bar" mode.

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Tim Mitchell
Reply to
Tim Mitchell

You want to drive it as a moving-dot or thermometer display? If the former, you could always use a 74HC42

That sure would be easy enough too. I guess you need 4 bits to include all-off and all-on states.

Reply to
Spehro Pefhany

"larwe" ...

Yes, there is. SN7445, the old NIXIE driver (open collector, 55V 80mA).

Put the LEDs in series, upper anode to a current source. The decoder can ground nodes sequentially. Or, instead of a current source, use a different resistor between each driver output and the node it drives.

Jellybean enough?

Regards, Arie de Muynck

PS: you will need of course need a LED supply of at least 1V + 8 x Vled ...

Reply to
Arie de Muynck

Sorry, it has to be a solid bar.

Reply to
larwe

Has to be thermometer. There are a load of analog parts designed for VU meters (I think) but I don't want to get too crazy with R-2R networks and such.

Exactly. It has to show all off through all on.

Reply to
larwe

Hmm, Digi-Key still stocks it... is it in production? TI's web site doesn't give a clue.

Definitely, thanks!

That's no problem, the board is driven by 24VDC.

Reply to
larwe

Good thing I looked at the answers before replying. That was precisely my solution. The major problem being that you will need a supply of over about 15 volts for reliability. You can make the current source with a reasonably well matched pair of pnps in a current mirror configuration, stabilized with emitter resistors if necessary. In which case you will need to allow about 1 volt of overhead for the mirror.

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Chuck F (cbfalconer@yahoo.com) (cbfalconer@worldnet.att.net)
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CBFalconer

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