power problem (newbie here!)

[BobK]

Hi Mister E,

Thanks for stepping in there. I kinda got off track with his original question!

BobK

[clocks]

Thank you gentlemen,

what I had (crucially!) forgotten to add, was that the program on the pic would stop working entirely when the more than two segments were on at a time. I have since found that it must be due to the PIC's current sourcing limitations (is this correct?). Regardless, I have added some CD4050BE buffers and now it all works fine.

I really appreciate your time and expertise. thank you.

Ps Not using a LCD as I don't have one! Beside, there's something appealing, almost 'retro' about 7 segment displays I find....

 
test code tags

[Acetronics2]

Hi Steve + Clocks

You do not use 105, but 4 x 105 mA ... ( no multiplexing !!! )

so, at least 2v * 420 mA = 850 mW to dissipate in the 7805 !!!

some cooling necessary then !!! ( 10° C/W will be Ok )

Alain

[clocks]

Hi Alain,

Indeed - no multiplexing (I need bright displays).

How do cool this down - or are there high rated voltage regulators out there?
I don't understand your last sentence; what is : 10° C/W?

thanks for your help!

[Acetronics2]

I don't understand your last sentence; what is : 10° C/W?

Hi,

It's the thermal resistance of the dissipator to use ... it's like Resistance's "Ohms" ... but for heat dissipation value.

That means it will heat at a rate of 10°C per dissipated Watt ... in your design, the temp of dissipator will be ( at blind sight ! ) ~ 25°C + (2 x 10°C) = 45°C

Alain