SD2000 combining both channels mod

[eclipse]

Please suggest a modification on the SD2000 to sum signals from both channels instead of taking signal from either one of these channels.




SD2000 Receiver.pdf

[kt315]

http://www.findmall.com/read.php?34,...131#msg-131131
seems there are much... from 2002...

[Xtrem]

Suming or subtraction ?? after the mod whαt audio tone you want to remains ? the high tone or the low ?
from what I understood you dont want the discrimination anymore.

[Altra]

To me S1 looks wrong. It will never allow U10b to toggle the AND gate 11A. S1 needs to be 3 pole so that there is an open position. As drawn U10b's output is either shorted to -5v 0r +5v.

[eclipse]

Maybe S1 Pin 2 must be connected to Pin 1 of CD4011 instead of Pin 2?
The schematic is the same as posted from ZED

[Altra]

Maybe a mistake or intentional? The way I remember it was supposed to work. Is you could use channel 1 or 2 seperately or both channels at the same time. The circiut works by rectifying the signal from each channel, U10b is a comparator which selects the channel with the greatest magnitude. If you have built this the way it is drawn it will either be high tone or low tone depending on the switch position. If you remove the switch it will be dual tone. Find a switch with on off on. Center off will be dual tone, +5v will select one channel and -5v will select the other.

Add: after looking at the original zed. If you zoom in on S1 you will see a vary light circle for center off position for dual tone. So the original drawing appears correct and the one you posted is incorrect.

[eclipse]

Sounds great! Thanks.
I saw now the circle which is the middle position on ZED's schematic.
I didn't see before that because the PDF it's low resolution and the circle is added manually, it is not ON-OFF-ON.

[Bill512]

the comments about the switch are correct, it should be a on-off -on type, as it actually is on the sd2000.
Now, about the high or low tone.
In sd2000, you can not get only a low, or only a high tone, by the switch (nor with any other action).
There is always a low/high tone in every channel , which channels are selected automaticaly by the machine, or manually by the user, via the swich.
The dual tone is by the (first) derivitive action, of the 2.2uF capacitor, same for both channels.
Every channel "produce" 2 type of infos, the first dirivitive signal and the rectified signal.
These are for the sound pitch variance and the sound intensity variance, respectively.
These actions are effectivelly a FM and AM modulation at the same time.
The rectified signals are used by the machine , to auto select the channel with the strongest signal.
For instance,for channel 1, U5A gives the output for the sound pitch and the U5B the output for the sound intensity. U7A buffers the rectified signal and U10B , compares the rectified signal.

[Bill512]

Please suggest a modification on the SD2000 to sum signals from both channels instead of taking signal from either one of these channels.

[ATTACH]39938[/ATTACH]

before any summation take place, you must ground balance the machine.
I do not see any (easy) way to ground balance the two channels, with their outputs mixed up.

[eclipse]

Probably ground balancing each channel is needed before switching to such mod, so it must be done so that the device can run normally or with both channels simultaneously/combined.
On older post by Woody suggest he used this method:

I left the gated switching as to allow for separate channel ground balance, I fed each channel in a dual gate mosfet BF966 I think it was for memory.

The Dual gate fet is being used as a el cheapo audio mixer, i added it dead bug style to the circuit board just as an experiment. Better results would be obtained by using an opamp mixer approach as it will give some gain.

[Mechanic]

Why????
What happens when you have a target with a rising pitch in ch1 and a lowering pitch in ch2? Add them together and you get.... Less or no signal!
None of the ML detectors combine ch1 and ch2, they are still used right up to the gpx5000 and you only ever here the channel that has the highest amplitude signal.

Cheers Mick

[eclipse]

Thanks Mick,
I saw this post by Woody some time ago and had me puzzled lately, but what you're saying makes more sense.

[Mechanic]

Careful with what you read from some time ago

Of course, if you wanted to do something tricky like combine 3 channels with specific timings for doing so, you could, but as to an advantage? It would take a lot of work.