14 Sep
2013
14 Sep
'13
8:19 p.m.
Hi all --
I'm attempting to get my 8/L talking to the outside world. It's
outfitted with the typical Teletype interface, which I'm attempting to
connect to a PC via acurrent loop to RS232 adapter.
Specifically, I've got one of these:
http://www.bb-elec.com/Products/Serial-Connectivity/Serial-Converters/Curre….
At the moment I have it configured (per the manual) assuming the 8/L is
an active loop device (i.e. the converter's transmit lines connect to
the 8/L's receive lines, and the 8/L's transmit lines connect to the
converter's receive lines). With this configuration I'm able to get the
8/L to send data to the PC successfully.
I'm not having much luck getting the8/L to receive anything from the PC,
however. If I put my multimeter in the loop, I see a current of about
40mA, which drops to between 30 and 37mA when the PC is sending data
(depending on what data's being sent). However, I'm not getting much of
anything onpin "E" of the W076 (Teletype Connector) board -- this is
supposed to be the "Logic Output" and I'm assuming that should be the
TTL-level data signal, correct?
I do see a very, very tiny signal (in the millivoltrange) on pin "E"
that matches up with the data being sent from the PC, but it's obviously
nowhere near the correct level. I've gone over the W076 board and
checked the related diodes and resistors for anything open/shorted. And
I actually did find a bad diode (fell apart when I desoldered one leg to
test) but replacing it made no apparent difference.
At this point I'm wondering if the loop configuration I have is
incorrect. I thought this was supposed to be a 20mA loop, but I'm
getting 40mA. I know very little about the fundamentals of current loop
stuff, so I could be way off here.
Anyone have any advice?
Thanks,
Josh
15 Sep
15 Sep
2:44 p.m.
Hi all --
I'm attempting to get my 8/L talking to the outside world. It's
outfitted with the typical Teletype interface, which I'm attempting to
connect to a PC via acurrent loop to RS232 adapter.
Specifically, I've got one of these:
http://www.bb-elec.com/Products/Serial-Connectivity/Serial-Converters/Curre….
At the moment I have it configured (per the manual) assuming the 8/L is
an active loop device (i.e. the converter's transmit lines connect to
the 8/L's receive lines, and the 8/L's transmit lines connect to the
converter's receive lines). With this configuration I'm able to get the
8/L to send data to the PC successfully.
That is normally the more difficult way to get working...
I'm not having much luck getting the8/L to receive anything from the PC,
however. If I put my multimeter in the loop, I see a current of about
40mA, which drops to between 30 and 37mA when the PC is sending data
(depending on what data's being sent). However, I'm not getting much of
anything onpin "E" of the W076 (Teletype Connector) board -- this is
supposed to be the "Logic Output" and I'm assuming that should be the
TTL-level data signal, correct?
I don't know this machine, but I've worekd on DEC current loop serial
interfces in PDP11s and the PDP8/e. I am going to assuem this was
originally intented ot link to a Teletype, a model 33 or something.
The transmitter side of a Teeltype model 33 is entirely passive. It's
just switch contacts. The idle state is 'closed' -- that is the 2
connections are shorted together by a pretty low resistance. THis opens
(to essentially infinite resistance) for each 'space' bit in the data stream.
Which means you should be able to trac signals by connecting a simple
switch to the 2 wires on the transmit loop of the PDP8/L in place of this
interface box, opening and closign the swtich, and seeing what, if
anything, changes state. Once you can get the right TTL levels at the
right point with that, you can then try again with the covverter.
I know nothign about this coverter. I assume the output is electrically
isolated from ground (and from the PC side). The DEC current loop input
is not isolated from ground, and if the output of the converter isn't
either this could cause all sorts of problems.
-tony
18 Sep
18 Sep
12:09 a.m.
Sorry to reply to my own post here, I had a bit more time to screw with
this this evening. Turns out it was a programming error (actually a
program entry error :)) that was (apparently) causing the 40mA current
instead of 20mA -- the little "echo" program I coded up wasn't properly
waiting for data to come in before echoing it back, so the 8/L was
constantly sending 377 back across the loop, which I'm assuming accounts
for the difference?
With this corrected, the loop is registering ~23mA idle, dropping to
19-20mA when the PC attempts to send data. Can anyone comment on
whether this sounds reasonable? Anyone have any advice? (Getting
desperate here :)).
Thanks,
Josh
On 9/14/2013 5:19 PM, Josh Dersch wrote:
Hi all --
I'm attempting to get my 8/L talking to the outside world. It's
outfitted with the typical Teletype interface, which I'm attempting to
connect to a PC via acurrent loop to RS232 adapter.
Specifically, I've got one of these:
http://www.bb-elec.com/Products/Serial-Connectivity/Serial-Converters/Curre….
At the moment I have it configured (per the manual) assuming the 8/L
is an active loop device (i.e. the converter's transmit lines connect
to the 8/L's receive lines, and the 8/L's transmit lines connect to
the converter's receive lines). With this configuration I'm able to
get the 8/L to send data to the PC successfully.
I'm not having much luck getting the8/L to receive anything from the
PC, however. If I put my multimeter in the loop, I see a current of
about 40mA, which drops to between 30 and 37mA when the PC is sending
data (depending on what data's being sent). However, I'm not getting
much of anything onpin "E" of the W076 (Teletype Connector) board --
this is supposed to be the "Logic Output" and I'm assuming that should
be the TTL-level data signal, correct?
I do see a very, very tiny signal (in the millivoltrange) on pin "E"
that matches up with the data being sent from the PC, but it's
obviously nowhere near the correct level. I've gone over the W076
board and checked the related diodes and resistors for anything
open/shorted. And I actually did find a bad diode (fell apart when I
desoldered one leg to test) but replacing it made no apparent difference.
At this point I'm wondering if the loop configuration I have is
incorrect. I thought this was supposed to be a 20mA loop, but I'm
getting 40mA. I know very little about the fundamentals of current
loop stuff, so I could be way off here.
Anyone have any advice?
Thanks,
Josh
12:49 a.m.
On Tue, Sep 17, 2013 at 09:09:46PM -0700, Josh Dersch wrote:
Sorry to reply to my own post here, I had a bit more
time to screw
with this this evening. Turns out it was a programming error
(actually a program entry error :)) that was (apparently) causing the
40mA current instead of 20mA -- the little "echo" program I coded up
wasn't properly waiting for data to come in before echoing it back,
so the 8/L was constantly sending 377 back across the loop, which I'm
assuming accounts for the difference?
With this corrected, the loop is registering ~23mA idle, dropping to
19-20mA when the PC attempts to send data. Can anyone comment on
whether this sounds reasonable? Anyone have any advice? (Getting
desperate here :)).
I may be misunderstanding you, but are you saying that you're using one
combined loop for both TX and RX? That's the right way to do RTTY
(with the old high-voltage 60 mA loop and Baudot machines) but the wrong
way to connect an ASR33 to a DEC machine (unless the 8/L is an oddball).
Separate loops for each -- and the ASR33's RX is just a solenoid, and
the ASR33's keyboard is just a switch.
Anyway you definitely want to do early testing by sending BREAK.
~20 mA idle (yes 23 is close enough), 0 mA breaking (or anyway vastly
lower) since you're supposed to be opening the (normally closed) circuit.
FWIW, here's the relevant snippet of a multi-line RS232/20mA converter
I've been gradually slapping together in my copious spare time (for
emulating DZ11Cs with RocketPorts etc.):
http://www.dbit.com/wilson/convert1.pdf
It's pretty standard stuff (DEC and BB both use similar circuits). This
shows two lines' worth, minus the RS232/TTL stuff (which is obvious, and
connects to the optoisolators), and it's jumperable for active vs. passive.
The only thing (as I'm discovering) is that it takes some fiddling to get
pullup values that work well over a wide range of bit rates (I've had to
slightly tweak the values from this schematic, I forget to exactly what, to
get up to 9600 but still not quite to 19.2K).
No guarantees that it would work with the 8/L, but it should be within a
mile. Optoisolation is probably overkill for connecting through a short
cable to a known circuit (with known ground reference). Even the
current-limiting (the 33-ohm resistors) is probably a bit much since no
one's trying to feed you infinite current. I went the other way (ASR33
attached to RS232 printer port on a PDT-11/150) eons ago with neither.
John Wilson
D Bit
1:08 a.m.
On 9/17/2013 9:49 PM, John Wilson wrote:
On Tue, Sep 17, 2013 at 09:09:46PM -0700, Josh Dersch
wrote:
I have it wired as in Fig. 2 in the PDF here:
http://www.bb-elec.com/Products/Datasheets/r2_Website-Only_0812DS.pdf. I
had thought that this was two separate loops, but given the behavior I
described earlier (with the 40ma while sending) perhaps I'm misreading
things...
Sorry to reply to my own post here, I had a bit
more time to screw
with this this evening. Turns out it was a programming error
(actually a program entry error :)) that was (apparently) causing the
40mA current instead of 20mA -- the little "echo" program I coded up
wasn't properly waiting for data to come in before echoing it back,
so the 8/L was constantly sending 377 back across the loop, which I'm
assuming accounts for the difference?
With this corrected, the loop is registering ~23mA idle, dropping to
19-20mA when the PC attempts to send data. Can anyone comment on
whether this sounds reasonable? Anyone have any advice? (Getting
desperate here :)).
I may be misunderstanding you, but are you saying that
you're using one
combined loop for both TX and RX? That's the right way to do RTTY
(with the old high-voltage 60 mA loop and Baudot machines) but the wrong
way to connect an ASR33 to a DEC machine (unless the 8/L is an oddball).
Separate loops for each -- and the ASR33's RX is just a solenoid, and
the ASR33's keyboard is just a switch.
Anyway you definitely want to do early testing by sending BREAK.
~20 mA idle (yes 23 is close enough), 0 mA breaking (or anyway vastly
lower) since you're supposed to be opening the (normally closed) circuit.
Thanks -- I'll give that a shot tomorrow when I have some time.
FWIW, here's the relevant snippet of a multi-line RS232/20mA converter
I've been gradually slapping together in my copious spare time (for
emulating DZ11Cs with RocketPorts etc.):
http://www.dbit.com/wilson/convert1.pdf
It's pretty standard stuff (DEC and BB both use similar circuits). This
shows two lines' worth, minus the RS232/TTL stuff (which is obvious, and
connects to the optoisolators), and it's jumperable for active vs. passive.
The only thing (as I'm discovering) is that it takes some fiddling to get
pullup values that work well over a wide range of bit rates (I've had to
slightly tweak the values from this schematic, I forget to exactly what, to
get up to 9600 but still not quite to 19.2K).
No guarantees that it would work with the 8/L, but it should be within a
mile. Optoisolation is probably overkill for connecting through a short
cable to a known circuit (with known ground reference). Even the
current-limiting (the 33-ohm resistors) is probably a bit much since no
one's trying to feed you infinite current. I went the other way (ASR33
attached to RS232 printer port on a PDT-11/150) eons ago with neither.
Cool! I'm hoping that I can manage to get the adapter I already have to
work, but it's good to see other options.
Thanks,
Josh
John Wilson
D Bit
1:36 a.m.
I think you mis-understand.
There is not two current sources. It the keyboard is in series
with the 33's coil and power supply, all you need to do to
send to it is provide a switch break.
A small drop across the input of a optical coupler is your
receiving end on the same loop. The 33 has the supply
already built in. You should not be providing additional
power. You may have to add resistance to bring the current
down to 20ma but you are not to be providing power.
Your sending should just be a switch.
Dwight
3:51 p.m.
I have it wired as in Fig. 2 in the PDF here:
http://www.bb-elec.com/Products/Datasheets/r2_Website-Only_0812DS.pdf. I
had thought that this was two separate loops, but given the behavior I
Assuming the schematic in that document is correct, that is, indeed, 2
separate loops, and it's what you want.
-tony
3:48 p.m.
Sorry to reply to my own post here, I had a bit more time to screw with
this this evening. Turns out it was a programming error (actually a
program entry error :)) that was (apparently) causing the 40mA current
instead of 20mA -- the little "echo" program I coded up wasn't properly
waiting for data to come in before echoing it back, so the 8/L was
constantly sending 377 back across the loop, which I'm assuming accounts
for the difference?
I realyl can;t see how the PDP8 sending anything (using its transmitter
and the receiver of the RS23 2adpater) can affect what happens in the
other loop. THe 2 sides should be totally independant.
With this corrected, the loop is registering ~23mA idle, dropping to
19-20mA when the PC attempts to send data. Can anyone comment on
whether this sounds reasonable? Anyone have any advice? (Getting
desperate here :)).
23mA is fine. But if 20mA is the 'off' state, tht is not fine. It could
be right for the mean current while data is being snet,
I have looked at the docuemnt you pointed out in another message. I
notice that this RS23 2interface powers itself from the RS232 handshake
lines. I am not overly happy with that, but... I owuld just check that
the right voltages do exist on the RS23e 2interface PCB.
I would then be inclinend to fidn some whay of cotnrolleing the TxD RS232
input ot the interface. Either by using the 'break' bit in the PC;s
serial chip or by disocnnecting that line from the PCB and using jumpers
to pull it high or low. WIth it low (-ve votlage), there should be 20mA
or some fliwiugn round the loop. 23mA is fine. WIth it high (+ve
voltage), there should be essentially no current flowing in the loop. If
you don't get this there is a hardware problem.
-tony
3:31 p.m.
On 09/15/2013 02:19 AM, Josh Dersch wrote:
Hi all --
I'm attempting to get my 8/L talking to the outside world. It's outfitted with
the typical Teletype interface, which I'm attempting to connect to a PC via acurrent
loop to RS232 adapter.
Specifically, I've got one of these:
http://www.bb-elec.com/Products/Serial-Connectivity/Serial-Converters/Curre….
At the moment I have it configured (per the manual) assuming the 8/L is an active loop
device (i.e. the converter's transmit lines connect to the 8/L's receive lines,
and the 8/L's transmit lines connect to the converter's receive lines). With this
configuration I'm able to get the 8/L to send data to the PC successfully.
I'm not having much luck getting the8/L to receive anything from the PC, however. If
I put my multimeter in the loop, I see a current of about 40mA, which drops to between 30
and 37mA when the PC is sending data (depending on what data's being sent). However,
I'm not getting much of anything onpin "E" of the W076 (Teletype Connector)
board -- this is supposed to be the "Logic Output" and I'm assuming that
should be the TTL-level data signal, correct?
I do see a very, very tiny signal (in the millivoltrange) on pin "E" that
matches up with the data being sent from the PC, but it's obviously nowhere near the
correct level. I've gone over the W076 board and checked the related diodes and
resistors for anything open/shorted. And I actually did find a bad diode (fell apart when
I desoldered one leg to test) but replacing it made no apparent difference.
At this point I'm wondering if the loop configuration I have is incorrect. I thought
this was supposed to be a 20mA loop, but I'm getting 40mA. I know very little about
the fundamentals of current loop stuff, so I could be way off here.
Anyone have any advice?
Thanks,
Josh
I have pair of M452 / W076 replacement boards that Vince Slyngstad offered some (
10?) years ago.
These convert the 8/L from current loop to RS232 output, and work great.
Maybe he still has some left ?
Jos
5:28 p.m.
Date: Wed, 18 Sep 2013 21:31:53 +0200
From: jdr_use at bluewin.ch
To:
Subject: Re: PDP-8/L current loop -> RS232 help
On 09/15/2013 02:19 AM, Josh Dersch wrote:
> Hi all --
>
> I'm attempting to get my 8/L talking to the outside world. It's outfitted
with the typical Teletype interface, which I'm attempting to connect to a PC via
acurrent loop to RS232 adapter.
>
> Specifically, I've got one of these:
http://www.bb-elec.com/Products/Serial-Connectivity/Serial-Converters/Curre….
>
---snip---
Depending on how you want to use it, you can have 1 or 2 current loops.
With nothing sent, 20ma is correct. It should go to 0ma for each data
bit, not 40ma.
If you make one loop, just use the supply in the 33. If you have
2 loops, another supply should be used.
1 loop for no echo and 2 if the computer echos what you type.
Check the specifications for your adapter.
Dwight
10:17 p.m.
From: Jos Dreesen: Wednesday, September 18, 2013 12:31 PM
I have pair of M452 / W076 replacement boards that
Vince Slyngstad offered
some ( 10?) years ago. These convert the 8/L from current loop to RS232
output, and work great.
Maybe he still has some left ?
I do. Coincidentally, I had been pricing components yesterday to build out
the remaining 10 or so of the baud rate generator cards (before I can't get
the parts any more). Assuming I order those parts, I'll have baud rate
generators as well as the half-dozen or so W076 replacements in stock.
(The boards are a bit embarrassing, as I've learned a lot about board layout
and such since then. They also lack gold fingers, which I'd definitely include
if I were to redo them. Should do the job, though.)
Has anyone noticed that prices on electronics components have soared
since the last time I did a board? Everything seems to be 3X-10X of what
I remember, at least from the non-surplus places. (Resistors for $0.10 each
in qty 100? Really??)
Vince
25 Sep
25 Sep
11:46 a.m.
For my 8/L I made a very simple adapter card. I added a card at D33,
where normally there would be a W076 Teletype cable card. The card is
such that I can swap interfaces back to a real teletype, if needs be.
(Note: View in fixed font!)
The Transmitter portion:
I added a wire from the M707 C31D2 (TTL Serial out) to D33D1
+-----------+-------- +5V
| |
4.7K Ohm Collector
| .
D33D1 --- 220ohm ------+-------- Base Q1, PNP Silicon
.
Emitter ----- 47 Ohm ---+--- RS-232 OUT
|
3.3 K Ohm
|
-12V (Regulated)
I built a duplicate of the above for the reader flag. The input was at
D33E1 (My notes don't indicate if a wire had to be added, but looking
at the machine, there was, from D32L2 to D33E1) and the output was to
RS-232 Pin 5 (Clear to Send - CTS).
The -12V Regulated was derived thusly:
-15V (Mine measures at about -20V)
|
330 Ohm 1/2 Watt
|
+------------------ -12V (Regulated)
|
12V Zener Diode Anode
|
Ground (Zener Cathode)
For the RS-232 Receiver, I did the following:
RS-232 In ------------ 3.3 K Ohm -------+------------- D33E2
|
3.3 K Ohm
|
Ground
There is/was, apparently, already a wire from D33E2 to the M706 input -
that would normally carry the signal to a W076.
This simple circuit works, in part, because the TTY input board clamps
to 0V and +5V, so all I had to do was to limit the current drawn from
the RS-232 interface).
Adjusting the M452 clock (location C33) was a little tricky: Use a
'scope or frequency counter. I used 4800 bps.
Looking back on it, it is quit possible that the inputs I already needed
were on D33H1 and D33M1, so the wires I added may not have been
necessary, but I haven't looked at it real hard.
Jay
On 9/14/2013 7:19 PM, Josh Dersch wrote:
Hi all --
I'm attempting to get my 8/L talking to the outside world. It's
outfitted with the typical Teletype interface, which I'm attempting to
connect to a PC via acurrent loop to RS232 adapter.
Specifically, I've got one of these:
http://www.bb-elec.com/Products/Serial-Connectivity/Serial-Converters/Curre….
At the moment I have it configured (per the manual) assuming the 8/L is
an active loop device (i.e. the converter's transmit lines connect to
the 8/L's receive lines, and the 8/L's transmit lines connect to the
converter's receive lines). With this configuration I'm able to get the
8/L to send data to the PC successfully.
I'm not having much luck getting the8/L to receive anything from the PC,
however. If I put my multimeter in the loop, I see a current of about
40mA, which drops to between 30 and 37mA when the PC is sending data
(depending on what data's being sent). However, I'm not getting much of
anything onpin "E" of the W076 (Teletype Connector) board -- this is
supposed to be the "Logic Output" and I'm assuming that should be the
TTL-level data signal, correct?
I do see a very, very tiny signal (in the millivoltrange) on pin "E"
that matches up with the data being sent from the PC, but it's obviously
nowhere near the correct level. I've gone over the W076 board and
checked the related diodes and resistors for anything open/shorted. And
I actually did find a bad diode (fell apart when I desoldered one leg to
test) but replacing it made no apparent difference.
At this point I'm wondering if the loop configuration I have is
incorrect. I thought this was supposed to be a 20mA loop, but I'm
getting 40mA. I know very little about the fundamentals of current loop
stuff, so I could be way off here.
Anyone have any advice?
Thanks,
Josh
1 p.m.
+-----------+-------- +5V
| |
4.7K Ohm Collector
| .
D33D1 --- 220ohm ------+-------- Base Q1, PNP Silicon
.
Emitter ----- 47 Ohm ---+--- RS-232 OUT
|
3.3 K Ohm
|
-12V (Regulated)
Sure you don't have collector and emitter switched on that diagram? If
you don't, you're using it "backwards"; lots of BJTs will work if you
swap C and E, but not as well as they will the right way around. (The
usual simplistic diagrams of BJTs make them look symmetric in this
regard, but as I understand it the diagrams are a simplification and
the actual geometry is not as symmetric as the diagrams make it look.)
Also, you're getting close to the RS-232 undefined voltage area there,
unless your RS-232 ground is not at the same voltage the +5 and -12
lines are referenced to; assuming Q1 drops half a volt and is otherwise
perfect, the open-circuit swing is between -12 and +4.27 (approx.), the
+ve end of which is close to the -3-to-+3 (IIRC) undefined area.
/~\ The ASCII Mouse
\ / Ribbon Campaign
X Against HTML mouse at rodents-montreal.org
/ \ Email! 7D C8 61 52 5D E7 2D 39 4E F1 31 3E E8 B3 27 4B
1:27 p.m.
On Sep 25, 2013, at 1:00 PM, Mouse <mouse at rodents-montreal.org> wrote:
The asymmetry is, in fact, the only thing that makes one end a
collector and the other end an emitter. If it were truly
symmetrical, it genuinely wouldn't matter which way you placed it.
But yes, it will (sorta) work placed backwards; I've had a number
of maddening debugging sessions that all boiled down to "I forgot
the standard pin ordering on a TO92 package", since the transistor
will *work* backwards, but is much weaker than expected.
- Dave
+-----------+-------- +5V
| |
4.7K Ohm Collector
| .
D33D1 --- 220ohm ------+-------- Base Q1, PNP Silicon
.
Emitter ----- 47 Ohm ---+--- RS-232 OUT
|
3.3 K Ohm
|
-12V (Regulated)
Sure you don't have collector and emitter switched on that diagram? If
you don't, you're using it "backwards"; lots of BJTs will work if you
swap C and E, but not as well as they will the right way around. (The
usual simplistic diagrams of BJTs make them look symmetric in this
regard, but as I understand it the diagrams are a simplification and
the actual geometry is not as symmetric as the diagrams make it look.)
3:02 p.m.
The asymmetry is, in fact, the only thing that makes
one end a
collector and the other end an emitter. If it were truly
symmetrical, it genuinely wouldn't matter which way you placed it.
But yes, it will (sorta) work placed backwards; I've had a number
of maddening debugging sessions that all boiled down to "I forgot
the standard pin ordering on a TO92 package", since the transistor
will *work* backwards, but is much weaker than expected.
I was 'led a merry dance' by this a few weeks back. I was working on a
1970s telephone answering amchine, a RecordaCall Bantam
The control system of that unit uses a number of interconencted SCRs
(thyristors). I found one that was certainly defective nad bought what I
believed to be identical replacements.
Upon fitting one, I got crazy results. That DCR seemed ot be turned on
all the time. Noting would turn it off. I disconencted the gate drive and
pwoered up. It was turned on. I shorted anode to cathode, it stayed
turned on when I removed the short. And so on.
After a lot of testing I found out what was going on. What I had fitted
was not an SCR at all, it was a PNP bipolar transistor.
The circuit had the cathode of the SCR conencted ot the -ve rail. A 470
ohm resisotor form gate to cathode. and a load resisotr from anode to the
+ve rail.
The SCR was in a TO5 metal can. So was the transistor I mistakenly
fitted. The cathode conenction (-ve rail) went to the mitter, the gate to
the base and the anode to the collector. Yes, that meant the trnasistor
was the wrong way round, but it still worked poorly. And that 470 ohm was
now between the point acting as a collector and the base. Not sruprisingly
that transistor was aturated.
Once I had fitted a real SCR, it all worked...
-tony
3:04 p.m.
But yes, it will (sorta) work placed backwards;
I've had a number
of maddening debugging sessions that all boiled down to "I forgot
the standard pin ordering on a TO92 package", since the transistor
will *work* backwards, but is much weaker than expected.
There is a standard pin ordering on the TO92 pacakge??? I am sure I've
seen just about all 6 possible permutations of the electrode conenctions...
-tony
4:07 p.m.
On Sep 25, 2013, at 3:04 PM, ard at p850ug1.demon.co.uk (Tony Duell) wrote:
I should have been clearer... standard ordering for the part I was
using (generally 2N3904 or 2N4401 or their complements, which all
have the same CBE pin ordering (or EBC, depending on how you look
at it), but I always forget which end is which.
You are certainly correct in that there's no true "standard"
ordering for TO92 parts, but for the parts I usually have on hand,
that's as close as it gets.
- Dave
But yes, it
will (sorta) work placed backwards; I've had a number
of maddening debugging sessions that all boiled down to "I forgot
the standard pin ordering on a TO92 package", since the transistor
will *work* backwards, but is much weaker than expected.
There is a standard pin ordering on the TO92 pacakge??? I am sure I've
seen just about all 6 possible permutations of the electrode conenctions...
2:17 p.m.
Or, maybe its NPN. I'd have to look at the card to be sure.
+5V is used with RS-232 all the time. I built this thing in 1985, on a
tight budget, long before there were inexpensive DC-DC converters. ;)
On 9/25/2013 12:00 PM, Mouse wrote:
+-----------+-------- +5V
| |
4.7K Ohm Collector
| .
D33D1 --- 220ohm ------+-------- Base Q1, PNP Silicon
.
Emitter ----- 47 Ohm ---+--- RS-232 OUT
|
3.3 K Ohm
|
-12V (Regulated)
Sure you don't have collector and emitter switched on that diagram? If
you don't, you're using it "backwards"; lots of BJTs will work if you
swap C and E, but not as well as they will the right way around. (The
usual simplistic diagrams of BJTs make them look symmetric in this
regard, but as I understand it the diagrams are a simplification and
the actual geometry is not as symmetric as the diagrams make it look.)
Also, you're getting close to the RS-232 undefined voltage area there,
unless your RS-232 ground is not at the same voltage the +5 and -12
lines are referenced to; assuming Q1 drops half a volt and is otherwise
perfect, the open-circuit swing is between -12 and +4.27 (approx.), the
+ve end of which is close to the -3-to-+3 (IIRC) undefined area.
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2:47 p.m.
[top-posting and no-trimming damage repaired manually]
Or, maybe its
NPN. I'd have to look at the card to be sure.
If so, then I'm astonished it works at all. If it's NPN and the pinout
markings are correct, then the output voltage swing should be
approximately the TTL range, never going very negative relative to
(circuit) ground. Also, the 4.7K resistor is in a weird place in that
case, whereas it makes perfect sense for a PNP with C and E switched.
Yeah, and the resulting serial ports tend to be unreliable, especially
when getting close to the cable length limits and/or with relatively
low-impedance input circuitry on the driven side.
+-----------+-------- +5V
| |
4.7K Ohm Collector
| .
D33D1 --- 220ohm ------+-------- Base Q1, PNP Silicon
.
Emitter ----- 47 Ohm ---+--- RS-232 OUT
|
3.3 K Ohm
|
-12V (Regulated)
Sure
you don't have collector and emitter switched on that diagram? Also,
you're getting close to the RS-232 undefined voltage area
there, [...]
+5V is used with RS-232 all the time. I built this thing in 1985, on a tight budget, long
before there were
inexpensive DC-DC converters. ;)
And no +12 easily available? Well, if it does what you want then it's
suitable for you; I'm just a little concerned about anyone else using
it for purposes different enough from your use case for the respects in
which it's borderline to matter.
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