Parallel to Series Converter Component Values?

[michael8554]

As for some reason I have some astronomy downtime.........

Set about updating my SC1 modded Toucam 740K

Flashed it to SPC900

Now looking at Parallel to Serial conversion

Trouble is Steve Chamber's original circuit uses a 470 Ohm series resistor:

http://www.pmdo.com/images/serialconv.gif

but other copies of the circuit use 4K7 (4700) Ohms:

http://www.pk3.org/Astro/index.htm?k3ccdtools_serial_port_adapter.htm

http://www.madpc.co.uk/~peterl/Equip/Mods/Fig22B.jpg

Now I appreciate the component values aren't super-critical, but this seems too much of a difference

So which is right?

Once this is sorted I will borrow some of YesYes's ideas to add a USB-to-Serial and stripped-down USB hub, to allow the camera to operate on just one USB cable.

Michael

[101nut]

I'd have thought 4.7k would be ok.

470ohms would drive it harder but obviously take more current ...

AndyG

[michael8554]

Thanks AndyG

All three sources have a pedigree, so I guess both values have worked in the past.

Michael

[fireshipjohn]

Hi,

Its just limiting the current into the base of the transistor, given a transistor gain (hfe) of about 100, then 4k7 would be fine.

John

[michael8554]

Thanks fireshipjohn

I tried 4K7 and it works, if anyone is interested.....:->

The rest of the "one USB only"  mod worked too.

That's a USB-to-Serial,  and the TouCam, into 2 ports of a stripped-down USB hub, all in a 80 x 60 x 40 project box.

Thanks to YesYes for the idea

Michael