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.
Jellybean barcode driver part?
Started by ●August 25, 2005
Reply by ●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 ●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 ●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 ●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 ●August 25, 20052005-08-25
> You want to drive it as a moving-dot or thermometer display? If theHas 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 ●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 ●August 25, 20052005-08-25
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!
