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.
In article , larwe writes
Two 74ACT138's would do it if you are happy to have "spot" mode rather than "bar" mode.
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.
"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 ...
Sorry, it has to be a solid bar.
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.
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.
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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