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you said the drive board is working fine, hope you tested it with the 7segment supplied by the kit maker.
if that part is right then what you are stuggling with, is to interface your large display.
5V may not excite enough voltage for the large display LEDs.
out puts A,B,...G , DP, DY1..DY4 are current sink, your buffer must be able to handle it,
if you have seriesly connected the LED in your display, then use a paropper voltage source only for the display and change all resistorsR1-R8 to limit the current (30mA), i beleive no need to use a buffer circuit, if i have understood it correctly.
Am using 12V to drive the big LEDs via MPSA64 Darlington transistors (see previously attached pic), kit works great.
Big LEDs require 8.8V @20ma (DP = 4.4V @ 20ma)
Mr Gibbs;
Went into Orlando to the Electronics Surplus place. Found some chips but they are mgf'd in Singapore (didn't have any made in USA) only number on them was 7406. So, will mess with them to see how they act, etc........
This conversion will take me a day or two, will be back with results, etc......
Tx's so much.........
hi,
The 74LS are lower power than the standard 74 series of IC.
I would try the 7406's in the circuit, if they load the PIC pins too much it will be necessary use 74LS06.
If you have any 14pin IC pcb style sockets I would fit them on the buffer, if you do have to change over the 06's it will be easier.
i think you can go for simple transistor buffering and get it done, i have just drawn an example how it can be, hope it might work. just see the attached.
i missed that point , so what about using a photo coupler like K3010? the transistor output can be like a switch. DY1...3 and A,B... all can be wired to each photocoupler input. it can drive 20mA directly.
hi,
If you connected the opt coupler emitter from the PIC pin to 0v, via a resistor then when the PIC pin went low [active] the opto detector would switch off, so the signal would be 'inverted'.
.
only four opto couplers can be used as shown with an inverter at the input, it can be one of the option for you incase if you couldnt solve the problem you have
Appreciate that.
Will keep circuit for future reference, etc.....
Tx's
Morning oxbo,
The problem with 'mbarazeen's circuit, is that you cannot turn OFF the lower transistors.!
hi oxbo,
The ULNs I suggested are compatible with the 12V that would have come from the 74LS06, if you get the datasheets you will see they require different input levels.
Can you post a datasheet for the LED's, I can then look at the LED curent for you.
EDIT:
Found the datasheet for the Green led.
The recommend continuous segment current is 20mA, can you measure the voltage drop across the series 120R.?
Remember the LED's are multiplexed so it would be possible to increase the 'pulsed' current thru the LED's on order to increase their brightness.