Im trying to control a 4x4 Led Matrix with 8 outputs on the K8055. I have designed a circuit…
But it may have a few kinks needed to be sorted out or there may be better methods if anyone can help me I would
appreciate it.
J1 represents the 8 outputs on the K8055 board.
The K8055 has open collector outputs, I.e. the behave as would a normally open switch–because of this the the NPN transistors you have selected will not turn on regardless of the K8055 output state.
Here’s a circuit using PNP transistors, I used a 2x2 matrix to keep it simple:
The box at the lower right represents the K8055 open collector outputs. with SPST switches shown to simulate the 8055’s internal activation of the outputs. Also note that each LED in the matrix has its own dropping resistor, this is to ensure that the brightness level is maintained regardless of how many LEDs are lit.
It is likely that Q3 and Q4 above are not 100% necessary as the maximum load on the column outputs will only be that of 4 LEDs–assuming they are not “super-bright” the maximum current should be within the 8055’s capacity.
In this circuit the columns are connected directly to the 8055 outputs:
The clamping diodes are also likely not needed as you are just switching LEDs.
One last comment, you do realise that this sort of matrix allows only lighting multiple LEDs in each row or column (or all of them)–I.e. you cannot for instance illuminate only row0/col0 and row1/col1 simultaneously. You could trick the human eye by strobing individual addresses, though IO don’t know that the K8055 will be fast enough to do that effectively?
It seems you do actually need the 4 transistors. The second circuit creates a constant voltage from V+ 9v to emitter of Q1 or Q2 depending on which is measured of P.D 8.18V. I’m not sure what the problem is but the best solution is that the transistors on the negative terminals are on.
Secondly despite the constant Voltage across the transistor and into the L.E.D they do not light up its seems that the interface board itself is creating resistance.
Another question on top of that, is it possible to use NPN transistors from the cathode of the L.E.D to GND?
Kinda like in here >>
I will test it and hopefully not blow anything up and somebody can then briefly explain the theory behind it.
General Transistor question…
To my belief NPN and PNP transistors had differentt pin layouts, my question is how come these data sheets
2N3904 NPN
http://www.fairchildsemi.com/ds/2N/2N3904.pdf
and
2N3906 PNP
http://www.fairchildsemi.com/ds/2N/2N3906.pdf
have the same pin allocation?
A hour or so later…
I checked to see how much voltage i’m getting from the output terminals and its only 0.66V i think that my problem is that theres not enough voltage on the base to get the current flowing.
[quote=“zero44”]It seems you do actually need the 4 transistors. The second circuit creates a constant voltage from V+ 9v to emitter of Q1 or Q2 depending on which is measured of P.D 8.18V. I’m not sure what the problem is but the best solution is that the transistors on the negative terminals are on.[/quote]The battery voltage is applied directly to the emitters of Q1 and Q2, it is not “created” by the circuit?
[quote]
Secondly despite the constant Voltage across the transistor and into the L.E.D they do not light up its seems that the interface board itself is creating resistance.[/quote]I have breadboarded the 2nd circuit and driven in with an 8055, check that everything is laid out and connected as in the diagram.
[quote]Another question on top of that, is it possible to use NPN transistors from the cathode of the L.E.D to GND?
Kinda like in here >>
[/quote]It would be, however you would need pull-up resistors on the K8055 outputs and the logic would be reversed. Also there would be no advantage in doing so PNP transistors are readily available.
[quote]I will test it and hopefully not blow anything up and somebody can then briefly explain the theory behind it.
General Transistor question…
To my belief NPN and PNP transistors had differentt pin layouts, my question is how come these data sheets
2N3904 NPN
http://www.fairchildsemi.com/ds/2N/2N3904.pdf
and
2N3906 PNP
http://www.fairchildsemi.com/ds/2N/2N3906.pdf
have the same pin allocation?[/quote]Though some NPN and PNP transistors do have differing pinouts, it is far more common for them to be the same as in the Fairchild documents you listed–the polarity of the current applied to the base, emitter, and collector differ between NPN and PNP, however the physical positioning of the pins in each case type is the same more often than not.
[quote]
A hour or so later…
I checked to see how much voltage i’m getting from the output terminals and its only 0.66V i think that my problem is that theres not enough voltage on the base to get the current flowing.[/quote]The output terminals of the 8055? If so then they have no output voltage by design, as they are open collector outputs. The emitter of the 8055 output transistor is connected to ground, collector to nothing but the output terminal, and the microprocessor drives the base to turn in off or on.
The equivalent of this circuit is shown in the simulated K8055 output shown in the maroon dashed line box on my diagrams.
