From: sleeper75se (sleeper75se_at_yahoo.se)
Date: 2002-05-09 03:26:40
Hi Peter, Dave and Joerg
(Yes, I am stacking replies again...)
--- In buildcheapeeg_at_yahoogroups.com, "Peter Charles" <cyberbiota_at_hotmail.com> wrote:
> I just recently joined this group, and have been surprised by
> the lack of posts.
This place used to be very talkative.
But, between reporting progress or asking for help, there is not
really much to say about the hardware right now. And I guess most of
the software people here are waiting for hardware to play with. "Dry-
coding" is quite difficult...
> I am working on some code to interface Palm-OS PDA's to
> a two-stage amp and mcu combination.
Feel free to share some of your work. It is always interesting to see
what others do.
--- In buildcheapeeg_at_yahoogroups.com, "Dave" <dfisher_at_pophost.com> wrote:
> ... My main focus now, though, is to get the entire device
> interface stable so that I can then move on to the wonderful
> world of filters and then finally engage the next phase which,
> for me, is the incorporation of sound feedback. For me, that's
> when the real fun truly begins!
Hi Dave, don't forget to add a scripting engine... and some cool 3D
animations, and games and a report generator, and ... and ... ;o)
Just kidding. It's good to hear that the software side is moving
along too.
--- In buildcheapeeg_at_yahoogroups.com, "Joerg Hansmann" <info_at_jhansmann.de> wrote:
> I have just downloaded it and have a few questions:
>
> What total current / power consumption does the circuit have ?
Hmm, there are no simple ways of measuring that without building
something I can put on the RS232 cable, but I did make estimates from
the datasheets:
I connect these to RTS:
A LP2980 low-drop regulator that draws 170uA at 1mA load,
a MAX987 comparator that draws 100uA at 1MHz switching (no load)
and a threshold voltage divider that draws 5V / 22kOhm = 230uA
Total: 500uA.
I connect the line driver (MAX1488E) to DTR (+) and TxD (-).
The datasheet specifies 180uA of quiescent current per rail, and it's
not easy to get below that with a discrete solution I think...maybe a
DS275 is better? It could fit too, provided it is fast enough.
> And what maximum baud rate ?
I use 115kbps, with the line idle about half the time. The signal at
the photo diode looks quite good, so that end could probably run
faster. Unfortunately, the MAX1488E is only guaranteed to handle
120kbps.
>
> What happens at increased temperatures e.g. 60 degrees Celsius ?
Don't know. I can check when I get the opportunity.
The datasheet for the diode I'm using
(http://www.elfa.se/pdf/75/07520232.pdf) reports a slight increase in
the dark-current from less than 1nA at room temperature, to 80nA at
75 degrees Celcius. Is this the kind of data you are looking for?
>
> Probly nothing, because you are using quite high photo currents
> up to 30uA.
>
> I am only asking because recently I have tried to build a POF
> receiver based on your 2 transistor design (slightly modified,
> 9600baud and ca. 10m fiber length) and ran into some difficulties
> at higher temperatures because the reverse current through
> the photo-diode increased and got greater than the photocurrent.
How about using a shorter fiber (< 1m) and longer RS232 cable? Or,
give more power to the LED? I use 10-15cm fiber, a 1.8m cable, and
5mA into the LED.
> (In the attachment is a schematic of a 1 op-amp solution with
> thermal compensation, that should work with 500nA photocurrent
> and up to 115200 baud. The simulation does not work as expected,
> because the TL071 model file from TI is definitely wrong (10 times
> supply current and 1/20 slew rate))
Well, since you have managed to make a very sleek design, and Spice
is unhelpful, why don't you just put it together real quick on a
breadboard or something? I don't see any reason why it wouldn't work
on a regular desktop-PC. I'm afraid that's the only suggestion I can
make...
Regards,
Andreas
This archive was generated by hypermail 2.1.4 : 2002-07-27 12:28:43 BST