Intermittent Problem with Circuit Design. Asking for Assistance.

[Jim Thompson]

Perhaps I didn't draw my circuit right? I'm not the best ASCII artist.

This is what I have made (thanks to Jim Thompson for the circuit I
stole and reconfigured):
+5V o------------------o
|
|
10K
|
o-----> OUTPUT
|
|/
Gnd---o-----|
| |
| |\
| E
_|_ |
330pF ___ |
| |
| |
| 5K
| |
| |
-5V/0V INPUT >-o-------o

course, my original problem was that it was intermittent. All I did
was add the capacitor, and it so far has been working 100% of the time.
Any thoughts? Or should I give up and never touch any components ever
again?

Maybe you had a bad solder joint? But your above circuit does not do
what you specified originally.

As drawn above, and working properly...

-24V Input --> ~0V Output
-12V Input --> ~0V Output

;-)

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice480)460-2350 | |
| E-mail Address at Website Fax480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

Anyone can be rude, but it takes a Democrat to be a real dirtbag.

 

[Derrick Tennant]

Well, I left out the zener diode, just for laziness.

I guess this would be the exact circuit I have:
+5V o---------o
|
|
10K
|
o-----> +5V/0V OUTPUT
|
|/
Gnd---o-----|
| |
| |\
| E
_|_ |
330pF ___ |
| |
| |
| 5K
| |
| |
o-------o
__|__/
/ /_\ (18V)
|
-12V/-24V INPUT >--o

....and the way it is now, during a -12V pulse, the output is +5V, and
during a -24V pulse the output is 0V.

This works for the application, because I then run the +5 through an
inverting buffer, which would give me my required correct output.

 

[Jim Thompson]

Well, I left out the zener diode, just for laziness.

I guess this would be the exact circuit I have:
+5V o---------o
|
|
10K
|
o-----> +5V/0V OUTPUT
|
|/
Gnd---o-----|
| |
| |\
| E
_|_ |
330pF ___ |
| |
| |
| 5K
| |
| |
o-------o
__|__/
/ /_\ (18V)
|
-12V/-24V INPUT >--o

...and the way it is now, during a -12V pulse, the output is +5V, and
during a -24V pulse the output is 0V.

This works for the application, because I then run the +5 through an
inverting buffer, which would give me my required correct output.

I'd put the threshold at mid-signal... zener = ~15V.

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice480)460-2350 | |
| E-mail Address at Website Fax480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

Anyone can be rude, but it takes a Democrat to be a real dirtbag.

 

[Rich Grise]

I thought your original spec was...

-24V Input --> +5V Output
-12V Input --> 0V Output
D'oh!

Common base is non-inverting.

Yes. I got it back-asswards: Here's an excerpt of the OP:
" The kicker is that at -24VDC it needs to be converted to +5VCD, and at
-12VCD, it needs to be at ground."

You need something like this...


+5V o-------o-------o
| |
| |
10K 10K
| |
| o-----> OUTPUT
| |
| |/
o-----|
| |
| |\
--- E
12V / \ |
| |
| o----GND
|
10K
|
|
INPUT >----o

Yeah, looks OK to me, except of course, I have to futz around with
everything:

+5V o-------o---------------o
| |
| |
10K 10K
| |
| o-----> OUTPUT
| |
| |/
o-------+-----|
| | |
| --- |\
--- / \ E
12V / \ | |
| | |
| `-------o----GND
|
10K 1N914, 1N4148, etc.
|
|
INPUT >----o

Cheers!
Rich

 

[Fred Bloggs]

I guess this would be the exact circuit I have:

+5V o---------o
|
|
10K
|
o-----> +5V/0V OUTPUT
|
|/
Gnd---o-----|
| |
| |\
| E
_|_ |
330pF ___ |
| |
| |
| 5K
| |
| |
o-------o
__|__/
/ /_\ (18V)
|
-12V/-24V INPUT >--o

...and the way it is now, during a -12V pulse, the output is +5V, and
during a -24V pulse the output is 0V.

This works for the application, because I then run the +5 through an
inverting buffer, which would give me my required correct output.

You need to watch pulling logic inputs negative. Since the application
requires no gain, a simple level level shift with over/under-voltage
protection is all that's needed:
View in a fixed-width font such as Courier.

..
..
..
..
.. +5V
.. | 74HCT14
.. -12 --- [10k] -- 5
.. | 20VZ | |\ |
.. | ---|>|--|<|---+----|>|--+---| o--- |
.. | / 1N914 1N914 | |/ |
.. -24 -- | --- 0
.. [100k]
.. |
.. ---
.. gnd
..
..
..
..
..

 

[Keith Williams]

Sorry. Should have said the above plus... or you'll have very weenie
base drive ;-)

Ohh, 5V BVebo. Ouch! ...wasn't considering reality. ;-)

Maybe the common base configuration is a good idea. Thanks.