PC connection causes line noise

Jim:

There is indeed a simple solution. You need to opto-isolate your hill circuits (other than the headset pair).

There are several devices you can try. ALGE makes a nifty opto-isolated adapter for your hill wiring (MC-18). TAG Heuer also makes a nice opto-isolator (HL 553). Lastly, Fred can fix you up with an RS-232 opto-isolator which goes between the TDC8000 and the serial port of your PC.

Any one of the above should solve your problem. Fred at Phoenix usually keeps the first two options in stock. The third option is available from Black Box.

Just remember that your headset pair cannot go through the opto-isolator, but all your timing points should.

You should have the grounding and punching of your hill wiring checked by a professional, as well.

James Broder
Broder's Skunkware Scoring & Timing Software
http://www.skunkware.tv

Are you using a desktop or notebook? Notebooks seem to be pretty immune to this problem because they don't need an AC ground connection. If a desktop, try using a ground lift to remove the AC ground connection from the power cable.

If that fails then the optocoupler between the timer and the PC is needed or moving the headset to another seperate pair.

Thank you, both, for your inputs. The computer tested was a laptop, and I experimented with a number of combinations of grounding the clock and computer, all with no change. The optical isolated interface between the 8000 and the computer seems the best idea.
The hill wiring is mostly all new this fall, with a new 18 pair cable and connection boxes. All of this was done by a couple of professionals (although working as volunteers). I myself am an electronics engineer, and I would like to understand just how this happens before I sweep it under the table with optical isolation. Is there a DC connection in the 8000 between the start circuits and the RS-232 outputs? Is there a schematic of the 8000 available?
Jim Gree

ALGE OPTODATA is in stock. This optocoupled device can be used for isolating the connection between the timer and the PC or between the timer and the GAZ display.

Adapter cables allow you to have the two uses available as needed.

The OPTODATA is powered from the timer and requires no internal 9v battery

This little thing between timer and Notebook works fine. It´s powered from the PC.

Greetz
Thomas