7-segment digits display only "8"

[DerStrom8]

**broken link removed**

Oh my, what a mess!

 

[ronsimpson]

Questions:
Q7 has no emitter resistor. It is not wired like the other transistors. Why?
What current are you expecting to go through the LEDs? With a 5k emitter resistor then the LED current is vary low!
Why R4?
How much current in D2, D4?

 

[sanjoy]

Why don't you use a bus??

To avoid simulation speed dropping below real time... Do not use resistors and transistors.. There is no need to sim the 5v regulator either..

yes ..so i avoid those in the simulation model as posted #18.
Does the 16f876A capable to multiplex 7 digits without flickering?
thanks u

 

[sanjoy]

Questions:
Q7 has no emitter resistor. It is not wired like the other transistors. Why?
What current are you expecting to go through the LEDs? With a 5k emitter resistor then the LED current is vary low!
Why R4?
How much current in D2, D4?

RA4 -- Output is open-drain type.
i missed to add resistor with Q7.
What current are you expecting to go through the LEDs? With a 5k emitter resistor then the LED current is vary low!
Why R4?--emitter resistor only for simulation. in real PCB it was removed.

 

[sanjoy]

Oh my, what a mess!

yes indeed. im not expert in that.

 

[JimB]

yes indeed. im not expert in that.

How much of an expert do you need to be in order to tidy up rubbish like this:

You don't know why your circuit will not work?
Neither does anyone else because they spend so much time trying to decode your abysmal schematic, they just give up and leave you to it.

JimB

 

[sanjoy]

JimB i agree with u. im sorry for spending ur time in a unskilled schematic.. pls accept my apology in this regard.

 

[ronsimpson]

Are the LEDs very dim? (not bright)?
Are you certain the transistors are connected correct? E,B,C

I question if this thing can light at all. If only one LED is on, current will flow through the emitter resistor. If all 7 or8 LEDs are on the the total current goes through the emitter resistor. I can't see how we can get more than 3V across 5k ohms so 600uA and with 6 LEDs on that 100uA per LED.

 

[sanjoy]

thank u for response, i agree so emitter resistor is omit in PCB drawing that given in #7..
i simulated the circuit in proteus, it performed well as per program.
problem occur when i soldered components in PCB, then power up, all digits display "8".
Does the 16f876A capable to drive 7 digits without flickering?
Should i use serially interfaced display driver ?

 

[DerStrom8]

You still need a resistor, otherwise you'll burn out your LEDs!

Best practice is to put individual resistors on each of the LEDs. That way you get the same current flowing through each one, regardless of the state of the other LEDs.

 

[Ian Rogers]

To all who are posting..

If the resistors are left off, it will only be for simulation... analogue parts play havoc when simming in real time...