SPC900 LX Mod

[JamesF]

I'm sitting here capturing Mars at the moment and my mind is pondering imaging, wandering a little as it does. Apologies if my typing is a little hit-and-miss. I *am* outside and typing in the dark

Anyhow, I was thinking about the control issues with the LX mod and the need for a separate switch to enable LX mode. As I understand it, this is because there are only two control lines with the USB->serial interface and the requirement is to turn three different things on and off.

Now my understanding of electronics is woefully poor, but it occurred to me that two control lines have four different states and that by running them into a demuxer you could effectively switch four different lines, effectively putting all the controls on one cable.

Is there any sense in this, or am I way off beam here?

James

[NEM]

I think the problem with using a demux is that you could only have one line 'on' at a time. Two lines do give you four states, but the LX inputs also need four states, exp on/off and amp on/off.

Because the inputs have to be driven in a fixed pattern, it should be possible to devise something using one line and a shift register together with some other logic. Each time the line was pulsed the circuit could switch to the next step in the pattern. The second line would be used to reset everything at the end of the sequence. But that would need special software to drive it.

It can be done but it gets very complex. I'd stick with the switch, that way you're compatible with the software already out there.

Regards,

Noel

[JamesF]

Ah, good point Noel. Thanks. I should have thought of that, really

James

[yesyes]

I agree with Noel.

Also, I noticed that the SPC900 also works in normal mode when the switch is in the LX position. So in my experience the switch is not even needed and can be left open.