From: Joerg Hansmann (info_at_jhansmann.de)
Date: 2001-06-06 01:25:52
Hi,
----- Original Message -----
From: Sajith Goonesekera <sajith_at_magix.com.sg>
To: <buildcheapeeg_at_yahoogroups.com>
Sent: Tuesday, June 05, 2001 5:09 PM
Subject: [buildcheapeeg] Test Fail
>Hi
>
>I have connected the electrode to my head and tried to get the signal.
>
>But I couldn't get any
1. Connect ch1+ and ch1- to a 10Hz 50uVpp calibration generator.
Do you get the right signal output at INA114 PIN 6 ? (should be 50mVpp)
>When I connect the CH1+ and CH1- I can see only 50Hz.
2. Connecting ch1+ and ch1- is not enough to get a zero signal, because
you do not provide a return path for the bias-current.
As a result the input stage will go into saturation and have a reduced
common mode rejection.
3. Connect ch1+ and ch1- together (directly at the pcb. That means without electrode cables)
and via a 20k resistor to R_LEG or VREF/2.
You should now get about 1uVpp noise RTI (referred to input) or 1mV noise
at PIN 6 of the INA114 and _no_ 50Hz line signal. (DC level referred to VREF/2 should
be less than +-50mV due to the amplified offset voltage of the INA114)
4. If you still get 50Hz in excess of 1uVpp (RTI) try to mount the pcb over a metal
ground plane connected to VREF/2 or AGND. Try to move the pcb more than 1..2 meters
away from line voltage cables, CRT-monitors, etc.
5. If the EEG amplifier works so far, connect shielded NF cables (thin coaxial cable)
of identical length (less than 1.5m) to the inputs. Connect the shields to the shield_1
output of the shield driver.
6. Now connect the inner wires (ch1+, ch1-) at the end of the cables together as described before
and via a 20k resistor to R_LEG.
You should now get similar results as in step 3
>When I connect RLD, 50Hz Disappear. But No signal at all.
What signal did you expect to get ?
>Any Suggestion???
>Have any one tried the live test.
No. Only with RS232EEG01.
You are absolutely the first one who built this circuit.
Regards,
Joerg
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