piclist 1998\10\07\000744a >
Thread: 4 digit auto-ranging frequency-meter.
face picon face BY : Sean Breheny email (remove spam text)

At 09:29 PM 10/6/98 -0500, you wrote:
>The displays are seven segment common cathode, it looks like a 4 digit
>multiplexed array, but four singles in paralell would work as well.
>The base resistors arent' critical, 470 ohm or 1k should work.

Do you really think THAT low? Even if the transistors were completely
saturated, I would expect the base resistors to be about 10 times the
segment resistors. If we used 470 ohm resistors on the bases, with a 5V
supply, we would have a base current of about 8mA. It would work fine, but
it would seem to me that for efficiency's sake, a few K would be better. It
would still throw the  transistors into saturation and save some power.

>The segment resistors are also uncritical, try 220-470. Depends much
>on the display efficiency.
>It's a cute project all right, hard to get less parts.


| Sean Breheny                   |
| Amateur Radio Callsign: KA3YXM |
| Electrical Engineering Student |
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