Jellybean barcode driver part?

[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.

 

[Tim Mitchell]

In article <1124984058.791172.108140@o13g2000cwo.googlegroups.com>,
larwe <larwe@larwe.com> writes

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.
--
Tim Mitchell

 

[Spehro Pefhany]

On 25 Aug 2005 08:34:18 -0700, the renowned "larwe" <larwe@larwe.com>
wrote:

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.

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.

 

[Arie de Muynck]

"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 ...

 

[larwe]

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

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.

 

[larwe]

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.

 

[larwe]

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.

 

[CBFalconer]

Arie de Muynck wrote:

"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?

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.

--
Chuck F (cbfalconer@yahoo.com) (cbfalconer@worldnet.att.net)
Available for consulting/temporary embedded and systems.
<http://cbfalconer.home.att.net> USE worldnet address!