Stumped novice needs advice

Trevor Rymell · Aug 29, 2005

Audioguru

Please ignore my previous post. I found the 7805 was stuffed. Sorry if I wasted your time. The circuit is fine now.

Many thanks to you, ljcox and Nigel for the expert advice.

Regards

Trevor

audioguru said:
Hi Trevor,
The circuit should work fine with your 4.8V supply. Anything more than 7V will exceed the absolute max voltage rating of the 74LS73.

When the output of the 74LS73 goes low to 0.5V or less. the base of the transistor will be pulled down to about 4.0V. The 680 series resistor will have at least 5.2mA through it and the transistor's base will get at least 4mA. With each segment of the display very bright at 30mA, seven of them draw 210mA. Therefore the transistor must have a current gain of 210/4 = 53. Its guaranteed minimum is about 60.

Typically, a BC327 will saturate at 0.25V with a 210mA load and 4mA of base current.
Maybe you have its emitter and collector pins reversed.
Maybe you have a weak BC327 transistor. General Semi sell them in batches of selected current gains and their BC327-40 has lots of gain. :lol:

ljcox · Aug 30, 2005

audioguru said:
I just opened Power Point for the very 1st time. I don't have a clue how to begin drawing anything. I was hoping a wizard or something would popup and assist me. :lol:

Attached is a PowerPoint file I made up to provide me with a library of symbols & circuit fragments that I copy and paste into new drawings.

Len

audioguru · Aug 31, 2005

Hi Len,
Thanks for posting your bits. I have a file that is full of bits and parts. I haven't converted it to a GIF or PNG yet so we can use it, since it is a RAR file extension. :lol:

ljcox · Aug 31, 2005

You're welcome Audio,

What I would like to know if it is possible to convert .gif or .png files to .ppt so they can be manipulated in PowerPoint.

You appear to imply that you know how to do this.

Len

audioguru · Aug 31, 2005

Hi Len,
I opened a GIF schematic with lots of text in MS Paint, copied it then pasted it into PowerPoint. No problem. :lol:

ljcox · Aug 31, 2005

Thanks, I had not thought of doing it that way.

Len

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