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Jellybean barcode driver part?

L

larwe

Jan 1, 1970
0
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.
 
T

Tim Mitchell

Jan 1, 1970
0
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.
Two 74ACT138's would do it if you are happy to have "spot" mode rather
than "bar" mode.
 
S

Spehro Pefhany

Jan 1, 1970
0
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?

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

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

Arie de Muynck

Jan 1, 1970
0
"larwe" ...
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.

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 ...
 
L

larwe

Jan 1, 1970
0
I need to drive an 8-LED bar graph from a 4-bit data source with the
Two 74ACT138's would do it if you are happy to have "spot" mode rather
than "bar" mode.

Sorry, it has to be a solid bar.
 
L

larwe

Jan 1, 1970
0
You want to drive it as a moving-dot or thermometer display? If the

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

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

larwe

Jan 1, 1970
0
Yes, there is. SN7445, the old NIXIE driver (open collector, 55V 80mA).

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

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

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

CBFalconer

Jan 1, 1970
0
Arie said:
"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?

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

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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