From: Brian Gr (brian_gr_at_hotmail.com)
Date: 2002-01-15 04:12:30
Hi,
I would calculate the required baud rate as follows:
10 bits / byte transmitted (start and stop bit plus 8 data bits)
As I understand, 6 data words and 1 sync word are sent every sample period
= 7 words / sample period
= 14 bytes / sampling period
that's 140 bits transmitted every sampling period
sampling period = 200 samples / second
minimum baud rate = 140 bits X 200 samples / second
= 28000 baud
That leaves 100% utilization of the rs232 link. Given that calculation, Joerg's requirement of 56K baud seems quite reasonable as a minimum baud rate. This would put the rs232 link transmitting at a bit below 50% utilization. This would transfer 6 data samples (10, 12 or 16 bits) at a sample rate of 200 samples / second.
Brian.
----- Original Message -----
From: Jim Meissner
To: buildcheapeeg_at_yahoogroups.com
Sent: Monday, January 14, 2002 4:17 PM
Subject: Re: [buildcheapeeg] Re: optical coupler
Dear Doug:
> they
> show a circuit for a handheld RS232 device connected via
> stereo mini-jack that was tested at 19.2k baud. The data
> sheet does not say this is the maximum rate. I have a few
> DS275s here. I will try to test at higher baud rates and
> let you folks know.
Yes, that was the only mention of Baud rate.
They said they tested it from 150 to 19.2 K baud.
Seemed a bit cryptic? I would read that to mean that 19.2 is the max.
> What baud rate are we shooting for? I
> keep hearing 115.2k mentioned, but do we need that? Why is
> that rate picked, because it's the max for most PC serial
> ports? I really don't think we need 115.2k.
I agree with you.
I keep mentioning that I used 9600 Baud to send 5 bytes at a 130 Hz sampling rate. Good enough I think.
Joerg is insisting on 56 K baud and Ardreas wants 115.2 K baud.
If building a 115.2 K baud "safe" 5 KV isolation voltage opto coupler will get this project moving forward, then I am all for it. That will be one more module in the chain that we won't have to argue over. As I stated before, you can always re-visit price and performance after "everything" works.
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: Doug Sutherland
To: buildcheapeeg_at_yahoogroups.com
Sent: Monday, January 14, 2002 2:29 PM
Subject: Re: [buildcheapeeg] Re: optical coupler
Hi Jim,
> Unless I read it wrong, the max rate of the DS275 is 19 KBaud
> and it still needs a power source larger than +5 volts
> ( a 9 volt battery )?
Say what? No, DS275 can operate on 5V only. It has a voltage
doubler inside to generate the higher RS232 voltages. I have
one running on 5V so I know it works. The data sheet says
that pin Vcc is for +5V (min 4.5 typ 5.0 max 5.5V). The data
sheet mentions that a 9V battery can be added to the DRV pin
for higher voltage, but I don't think we need that. I have a
uC connected to PC (RS232) with DS275, no problems at all, 5V
only operation. The reason that I suggested DS275 in the
first place was because it was low power, possibly low enough
to get power from the PC serial port. Regarding baud rate,
there is no mention of max baud rate in the data sheet, they
show a circuit for a handheld RS232 device connected via
stereo mini-jack that was tested at 19.2k baud. The data
sheet does not say this is the maximum rate. I have a few
DS275s here. I will try to test at higher baud rates and
let you folks know. What baud rate are we shooting for? I
keep hearing 115.2k mentioned, but do we need that? Why is
that rate picked, because it's the max for most PC serial
ports? I really don't think we need 115.2k.
-- Doug
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