13 replies to this topic

[Eric Burdo]

Once upon a time, I worked for McDonalds. They have a mini "computer" that runs the deep fryers. One of the fryers died, and I convinced the company to let me have the board from it. (well, actually 2 of them). It contains a 16 segment "alphanumeric" display. Where would I get started in how to control one of these? I think I'd have to use "shift registers" to make it work? Am I correct?

[Eric Burdo]

Just an FYI - I'm going to start with some of the stuff found here: http://www.arduino.c...ithHardware#LED It's for the Arduino, and has some items on using the 7 Segment and then "more segment" LED displays.

[hari]

I think I'd have to use "shift registers" to make it work? Am I correct?

The correct answer is yes, you need shift registers or a 7-segment display driver and probably a few transistors to help with the current load.
However... depending how many "digit"s you're trying to control, there may have enough pins on the Netduino.
Take a look the fourth post on this thread. It was an experiment I did a while ago on the Arduino. Multiplexing is cool.
http://www.arduino.c...um=1265669651/0

[CW2]

However... depending how many "digit"s you're trying to control, there may have enough pins on the Netduino.

Please note you can easily chain the shift registers (e.g. for 74x595 connect serial output Q7' to the next IC's serial input), so you need only three pins to control large number of individual LEDs (or LED segments): serial data input of the first register, clock and latch wired together for all the registers. For multiple digits, another register can be used to multiplex the common electrode (depending on display type it is either anode or cathode).

[Eric Burdo]

Ok... to shift registers... does that require another chip to use? I've seen some at SparkFun and such. Or can I do all the register shift stuff straight from the Netduino? As far as enough pins... the Netduino doesn't have enough. I'd need 18 pins I think (17 segment Alphanumeric display, with a 2nd display, so 18 pins?)

[Chris Walker]

As far as enough pins... the Netduino doesn't have enough. I'd need 18 pins I think (17 segment Alphanumeric display, with a 2nd display, so 18 pins?)

Quick note... Netduino has 20 digital (the 14 dedicated digital pins--plus the 6 analog/digital pins). The first four "analog" pins (A0-A3) only drive 2mA however.

Chris

[CW2]

Ok... to shift registers... does that require another chip to use? I've seen some at SparkFun and such.

You can use 74HC595 serial to parallel shift register. As I wrote above, you need only three pins to control such a register, for 17 segment LED display I would use two chained registers (16 segments) and then a separate pin (with a transistor) to control the 17th segment (the dot, if used at all?). It should be also possible to drive the display with only one register, by multiplexing two 8-segment groups.

[CW2]

Please have a look at Arduino - ShiftOut tutorial to get the idea - a LED represents single display segment.

[CW2]

It contains a 16 segment "alphanumeric" display.

It would help to get a bit more details about the part:

• Does it have any part number? If not,
• Do you know the common electrode? Anode or cathode?
• Do you know forward voltage of a single segment? If not, what is the segment color?

[Eric Burdo]

It would help to get a bit more details about the part:

• Does it have any part number? If not,
• Do you know the common electrode? Anode or cathode?
• Do you know forward voltage of a single segment? If not, what is the segment color?

All I know right now... is that I scavenged these from a deep-fryer controller. Haven't found any part #'s yet.

I'll pull it out later and look again... see if I can find some info for you.

[CW2]

I'll pull it out later and look again... see if I can find some info for you.

I should be able to help you with connecting the LED display to Nedtuino and perhaps the controlling algorithm for the register, multiplexing etc. I am asking for details, because they may significantly affect selection of the components: for example, if the display is big, it can have a segment composed of multiple LEDs, then you'd probably need a power version of the shift register that supports higher voltage or current; the common electrode determines what kind of transistor (NPN or PNP) can be used to switch it; and forward voltage has to be known to calculate the current limiting resistor (the register itself has some voltage drop, which should be included in the formula etc.). The LED voltage can be guessed from its color, see the Colors and materials table.

[Eric Burdo]

Found it... and here is the data page about it: http://www.datasheet.../LC5442-11 LEDs There is a datasheet there... I have like... 10 of these, soldered onto the deep fryer control boards. I've removed one... I'll be learning to read a data sheet, since most of it is greek to me. I got the 7 segment working (direct pin mapping) with the Netduino. I'll writeup that, and then start playing with this new piece.

[Szymon]

Hi Eric, Maybe this example will help you get started: http://geekswithblog...nking_leds.aspx It shows how to use a shift register to talk with two 7 segment LED modules.

[Eric Burdo]

Hi Eric,
Maybe this example will help you get started:
http://geekswithblog...nking_leds.aspx

It shows how to use a shift register to talk with two 7 segment LED modules.

Thanks Szymon! I'll pick up a couple of shift registers this week (I don't have any in my collection of parts). I'm hoping the Netduino Plus shows up at MakerShed soon... I'll order everything from them.