Is this Sch right??

[kentken]

Bellow is my Sch of my project.
Are the 2n3904 the best choise?
Is there a array that would work better?
What is the lowest value for the display resistors?(max brightness)

Did I miss anything?

Thanks
Kent

 

[Nigel Goodwin]

Bellow is my Sch of my project.
Are the 2n3904 the best choise?

I would suggest PNP transistors would be a far better bet, with emitters to +ve, and resistors in series with the bases. This would give you more voltage to the displays (approaching 20% more) - you would need to alter your code to make them active low, rather than active high.

Is there a array that would work better?
What is the lowest value for the display resistors?(max brightness)

The lowest value resistor is a simple ohms law problem, based on the supply voltage (minus the drop across the top and bottom drivers), and the maximum current handling of the displays. As the displays are multiplexed, you can multiply the maximum current by the number of displays - as long as it never locks up!.

 

[kentken]

Once again, thank you.
I will change to PNP, pulling the base to v+.

I'm not to clear on the calculations.
Steady current of: 30ma
Peak current of: 150ma
voltage: 2.0
Max v: 2.5
6 digits multiplexed
= :?:

Is there anyother suggestions you have?

Thanks
Kent

 

[GraveYard_Killer]

i wonder what are connected to the other ends (VCC or VSS?) of the Dog,Knoter Sensor,Counter,Reset, and Stroke Reset. Do u have plans to put pull up resistors or pull down resistors?

 

[kentken]

They are like that because of the link to the PCB drawing. They are hooked to GND and the pull-ups in PortB.

 

[kentken]

Nigel, Do I really need the ULN2003 to sink the current, or will the Pic handle it?

kent

 

[Nigel Goodwin]

Nigel, Do I really need the ULN2003 to sink the current, or will the Pic handle it?

You need the ULN2003!.

In answer to your question above about current, as the display spec you gave says 150mA peak - I would calaculate the resistor values to give 150mA.

 

[kentken]

So,
3v/100ma=30 Ohm
3v/150ma=20 Ohm

Is this right?
I'm still new to this side of electronics.

Thanks
Kent

 

[motion]

I would suggest PNP transistors would be a far better bet, with emitters to +ve, and resistors in series with the bases. This would give you more voltage to the displays (approaching 20% more) - you would need to alter your code to make them active low, rather than active high.

Yeah, but you would need one more resistor at the base pin for each transistor. You don't need to increase the voltage because the LEDs turn ON at around 1.5V. You would still need the resistors in series with the LEDs to limit the current when using PNPs.

 

[Nigel Goodwin]

So,
3v/100ma=30 ohm
3v/150ma=20 ohm

Is this right?

Yes, I would suggest using 22 ohm, which is a standard value.

 

[kentken]

I found another display that is brighter, it is 5600ucd, the other was 3900ucd.
They are only in single digits, but....they are brighter. I was trying to use up the others, but...

These have the same power specs.

Would you still suggest using PNP transistors?

Below is a layout with PNP's. If this is the way to go, please take a look.
What should the values on the R2's and the R1's be?

Note: R2-R8 on bottom are not correct value, should be 22

Thanks
Kent

 

[Nigel Goodwin]

Below is a layout with PNP's. If this is the way to go, please take a look.
What should the values on the R2's and the R1's be?

R1 might, or might not, be needed - it usually won't be.

R2 isn't critical, it simply needs to pull enough current through the base of the transistor to saturate it - 1K or 2.2K should be fine, you could use the same value for R1 if you wanted to fit them.

 

[kentken]

Is there a IC that would function here?
Sugestions?
Cheaper then single parts?

Thanks
Kent