Electronic scoreboard project

Thread Starter

mike_crawford

Joined Jan 21, 2010
20
Hello, I am looking to convert an electronic scoreboard from my table hockey into a four sided scoreboard, which means I have to add 6 additional 7-segment LEDs (2 for each of the other three required sides). I figured out to 'tap' into the data signals and split them across these other 6 LEDs, but the current from my adapter appears not to handle the required amount to illuminate all LEDs to a bright enough level for good viewing. Rather than change the original adapter (6 Vdc /200mA) and possibly affect the circuit board of the scoreboard, I was wondering how difficult would it be to add a secondary circuit with its own adapter that was specifically designed to provide enough current to power all the LEDs, while the original adapter powers the circuit board. Reason being I don't want the circuit board to draw too much current through its microprocessor or other components, and burn out while trying to power these additional LEDs.
My thoughts were to use transistors connected to each of the primary circuit's data lines that act as switches into the secondary circuit, allowing amplification of the current through the LEDs in the secondary circuit, and therefore not overload the primary circuitry in any way.

Any help would be appreciated :)
 

hgmjr

Joined Jan 28, 2005
9,029
Have you managed to reverse engineer the existing circuit to create a schematic for it? If so, it would be helpful for you to post it here.

hgmjr
 

Thread Starter

mike_crawford

Joined Jan 21, 2010
20
Nothing official yet, but I all I really need is to figure out out to take a 7-segment LED ... amplify the current its getting within a circuit so I can clone the data its receiving to another 7-segment LED. Final picture... instead of one 7-segment LED, I would now have two (or more) all displaying the same info. DC op amps perhaps?
 

SgtWookie

Joined Jul 17, 2007
22,220
You need to post the existing circuit first. Otherwise, we really don't have much to go on.

Odds are that the original power supply could be replaced with a more capable unit, but unless we know what you have now, you're more likely than not to simply fry what you have.
 

retched

Joined Dec 5, 2009
5,208
It may be easier to half the value of the resistors for the existing 7segs LEDs and then just wire the new ones into the existing ones.

BUT, the schematic and power specs would be the determining factor.
 

marshallf3

Joined Jul 26, 2010
2,358
The existing display is probably driven with a single LED in a multiplexed situation. It also probably won't be capable of sinkng enough current to drive anything ore than the one display.

While you could build buffer amps for every segment, if you had the schematic it would be far easier to duplicate the circuit from the decoder/driver IC and put the resulting circuits in parallel.

Can you get into the thing far enough to see what's driving the current LEDs? If the dsiplay goes to a single or small group of ICs get the number(s) off them, that would be of some help if a schematic isn't available.
 

Thread Starter

mike_crawford

Joined Jan 21, 2010
20
Ok here is the best I can do for now (I will still attempt a schematic but it may take me awhile, as this is dual layered, and I don't have a lot of experience with more complicated circuits like this), its an image of the front and back of the scoreboard circuit. Its quite old (1989) and in very rough shape but it still (for now at least) works great.



Its controlled by a PIC micro controller. Note the blue wire hanging from the bottom of one of the eight grouped 220 Ohm resistors. This is where I intercept the current carrying the data that lights up each of the 8 segments (including DP). Specifically the blue wire connects to the 'E' segment for all 4 LEDs. Its my interpretation with these type of circuits that the LEDs, while appear to be on all the time, are actually being interlaced (multiplexed?) via the 4 transistors near the top (1 per LED) of the circuit board. Ultimately I would like to rebuild this circuit before it degrades any further and stops working, while adding the extra LEDs at the same time.
 

MMcLaren

Joined Feb 14, 2010
846
Hi Mike,

Looks like "direct I/O" drive on the segments. You need to determine if the displays are common cathode or common anode. Do a search on the display part number and also note the number on the driver transistors.

One way you might expand the displays is to remove the segment current limiting resistors and add a daughter card with a 500-ma sinking or sourcing driver IC (depends on the type of displays). You'll need to duplicate the displays and driver transistors for the other three sides. The outputs from the new segment driver IC will drive the segments on all four displays (through a set of segment current limiting resistors for each display).


Regards, Mike
 

Thread Starter

mike_crawford

Joined Jan 21, 2010
20
Hi Mike,

Looks like "direct I/O" drive on the segments. You need to determine if the displays are common cathode or common anode. Do a search on the display part number and also note the number on the driver transistors.

One way you might expand the displays is to remove the segment current limiting resistors and add a daughter card with a 500-ma sinking or sourcing driver IC (depends on the type of displays). You'll need to duplicate the displays and driver transistors for the other three sides. The outputs from the new segment driver IC will drive the segments on all four displays (through a set of segment current limiting resistors for each display).


Regards, Mike
The LEDs are common anode
driver transistors are type 2N3906

What would be a suitable 500-ma sinking or sourcing driver IC (part #?) for this approach?
 

MMcLaren

Joined Feb 14, 2010
846
Just realized you'll need to invert the segment signals to use a ULN2007 (7-bit) or ULN2803 (8-bit) sinking driver IC (sorry)... Let me think about this...

Regards, Mike
 
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