From: yaniv_vi (yaniv_vi_at_yahoo.com)
Date: 2002-01-02 15:07:13
hi
the ir option you just mentioned , sounds like a great soultion to the isolation problem .
tell me , what was the distance between the 2 boards (bm , and isolation card ) ?
could it be one meter at 9600 baud ?
thanks yaniv
--- In buildcheapeeg_at_yahoogroups.com, "Brian Gr" <brian_gr_at_hotmail.com> wrote:
> Hi,
> I built a BrainMaster when it was an open design. I went through similar issues with power
and isolation. Here's what I did with the bm, maybe they could be of some use in this design:
>
> I put only one connector on the unit, a 25 pin D connector. Depending on which of two
cables were plugged into this unit, one could either operate the unit or charge the internal
6 nicads in the unit, but one couldn't run the unit with the charger, at least with these
connectors.
>
> The nicads were connected to the 25 pin D connector in 3 battery pairs. The eeg inputs
were connected to the 25 pin D connector. The input and ground and isolated serial was
connected to this connetor as well.
>
> One D connector/circuit was used to charge the batteries. It connected a wall wart to a
couple of resistors to charge the internal batteries. You couldn't operate the unit when
this connector was connected as the rs232 and eeg inputs were not connected on this
connector/circuit.
>
> A second connector/circuit was used to operate the unit. By connecting pins on this
connector, the three pairs of batteries were connected in series and fed to a voltage in
and ground pin on the 25 pin connector. This powered the unit. This connector had eeg inputs
and ref ground and isolated rs232 connected as well.
>
> The Vin and ground were available on the connector, so I suppose someone could or would
think of connecting an unisolated supply to this input and not using the internal batteries.
Well, I'm no dummy, I never would.
>
> To isolate rs232, I used 2 pairs of ir leds and integral ir recievers from Digikey. They
were Fairchild parts. Current Digikey part #s are QSE158-ND ($1.42, qty 1)
(http://rocky.digikey.com/scripts/ProductInfo.dll?Site=CA&V=46&M=QSE158) for the logic
detector and QEE113-ND ($.74, qty 1) (http://rocky.digikey.com/scripts/ProductInfo.dll?
Site=CA&V=46&M=QEE113) for the ir diode. The reciever has built in circuitry to generate
logic out from IR in. The leds and current limiting resistor were connected to the tx on
both sides and the logic detector was connected to the rx on both sides. Pointing the
appropriate led / detector pair at each other allowed isolation. The BM board had one pair
and the isolation board had another pair. You might think of these as optoisolators in two
packages. You could control the distance between the pairs to increase isolation. There was
no problem running 9600 baud across these parts.
>
> If I was to build this again, I would put a seperate connector for the isolated RS232 to
increase the distance between the isolated and non isolated portions of the circuitry. On my
brainmaster, the isolated and non isolated circuits go to the same connector, with a couple
of blank pins between.
>
> Brian.
This archive was generated by hypermail 2.1.4 : 2002-07-27 12:28:36 BST