From: Jim Meissner (jpmeissner_at_mindspring.com)
Date: 2002-01-03 19:54:42
Dear Brian:
> Current Digikey part #s are QSE158-ND ($1.42, qty 1) for the logic detector and
> QEE113-ND ($.74, qty 1) for the ir diode
That looks like a great solution! How far apart can these parts communicate? I think 1 inch in air is about 10 or 20 KV? This would solve the HiPotand isolation problems if you used two separate circuit boards. I am going to buy some to try. Could you share some more details of your circuit?
BTW I have drawn up the opto isolator circuit that I used years ago with mybrain monitor system. It is listed as Iso01.gif on the Brain Wave Monitorpage of my website. Let me know what you think of that?
Juergen P. (Jim) Meissner
Check out my Website at www.MeissnerResearch.com
Read about the benefits of the Brain State Synchronizer sounds for improving your life and health.
----- Original Message -----
From: Brian Gr
To: buildcheapeeg_at_yahoogroups.com
Sent: Saturday, December 29, 2001 8:57 PM
Subject: [buildcheapeeg] Power/isolation issues...bm solution
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 txon 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.
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This archive was generated by hypermail 2.1.4 : 2002-07-27 12:28:36 BST