> "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!
Reply by larwe●August 25, 20052005-08-25
> 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.
Reply by larwe●August 25, 20052005-08-25
> 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.
Reply by larwe●August 25, 20052005-08-25
> >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.
Reply by Arie de Muynck●August 25, 20052005-08-25
"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 ...
Reply by Spehro Pefhany●August 25, 20052005-08-25
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.
Reply by Tim Mitchell●August 25, 20052005-08-25
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
Reply by larwe●August 25, 20052005-08-25
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.