I've seen some outputs, running closed-loop, spike several volts when another channel railed. It has to do with multi-collector shared current sources saturating, I think. I'm pretty sure it was the National parts. I recall Jim saying that some peoples' 324's do it, and some don't. Anyway, it's another interesting hazard. The 324 is a really terrible opamp; massive crossover distortion and ghastly substrate diode issues, too.
Might be the same problem. I used 324's as comparators (single-slope adc's in an electric meter) and had terrible interactions. Dropped in an LF347 and everything worked.
Yep. That's part of what provoked me, at GenRad, to de-list Motorola as a vendor for 324's.
Terrible distortion. My cure, for active filters, was to load the output to class-A.
Not sure what you're referring to here. Pulling an input way below ground??
...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC\'s and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |
America: Land of the Free, Because of the Brave
You could perhaps use a PIC675, it has a 10bits AD IIRC, internal osc. If you grab reference and voltage divider-pot from the same supply, and the required output freq is not too high, then this can be very stable. The internal osc is 4MHz IIRC, and can be software calibrated. If you need more accuracy, use a xtal, a bunch of those on one xtal should work. Advantage: No capacitor needed, only the PIC and the pot. Several kHz should be possible, if not more. And pins left for other fun things, micro-power too. Low supply, hows' that?
Actually it's in the current datasheets of the LM393 as well! I got bitten by this just yesterday in a circuit where the 393 goes haywire when the input goes negative, fed through a 50k resistor, despite my having added clamp diodes. I put in a Schottky diode but haven't tested this yet.
Very annoying. I don't have any resonable negative rail to work with (just
-40V), there's little space on the board etc. I can yank up the input series resistor and pray to get away with the Schottky. This is a one-off.
0.3V is weird. I always figured I'd pretty safe with a diode drop. Not so.
Hmmmm! -0.3V was a CYA thing, it took a vBE below ground to disrupt... and I've only seen issues with a single OpAmp, not the whole package... UNLESS: OpAmp railing tripped the PNP mirrors on certain brands ??
...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC\'s and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |
America: Land of the Free, Because of the Brave
It was not far from 0.3 on the National parts, and all four opamps would rail, one polarity at first, then they'd rail in the other direction as the clamping current was increased. I wouldn't joke about a thing like this.
Of course I thought about that, especially since I could just read out, say,
10 pots via a multiplexer and control 10 timing channels that way.
Problem is: I've never gotten my head around any embedded design, so I'm staying in the analog domain.
BTW, the gadget in question is a "sequencer" that actuates some relays after individually programmable delays. It's going to be used for special effects in a film studio.
The LM35 family of temperature sensors is similarly delicate. The thing about them is that National *tells* you to pull the outputs below ground to read negative temperatures. My advice is to not do it. If you want to read below 0C, use the Fahrenheit version and don't pull it below ground.
As in one-shots? Ah, then you may want this instead:
formatting link
Some day I should redraw that with a two-transistor flip-flop.
Operation: rising edge causes Qbar to fall. Capacitor charges by about 3V, then the feedback junk flops and the capacitor discharges. And of course, other values may get better performance (like for minimum flop current from R_T).
Heck, a monostable can be made with two transistors, around four resistors and a capacitor. This is kind of a verbose version of that.
Tim
-- Deep Fryer: A very philosophical monk. Website @
I haven't done any discrete stuff in years, but I recall using Ge diodes for such occasions ;-)
...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC\'s and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |
America: Land of the Free, Because of the Brave
On a sunny day (29 Nov 2007 17:12:31 GMT) it happened Robert Latest wrote in :
Not to critise, but as a hint, long time ago I designed some video stuff with analog and normal logic, it was boards full of chips (counters, comparators, what not). Then I got more orders, and replaced the whole thing with a PIC microprocessor. That made things more reliable, the hardware simpler, the cost much lower, the stability better, and the profit bigger, much bigger. Also if there is a problem, you can simply update the soft. I dunno if you can program a PIC, but if not, then have a go some day. It is worth it.
Especially in the 'film studio', I am familiar with that environment, if they see something, then they also have a hundred more ideas of things they want. Re-programmable logic may just allow you to provide it to them fast.
How about 10000:1? A truly remarkable chip is the precision LM331 voltage to frequency converter- .01% linearity (4 decimal digits in a cheap old chip).
The 555 is crap, I wish it would go away. It's only advantage is wide operating voltage range. I much prefer the TTL timing chips over it: HC123, and HC221 for lower precision applications.
--
/* jhallen@world.std.com AB1GO */ /* Joseph H. Allen */
int a[1817];main(z,p,q,r){for(p=80;q+p-80;p-=2*a[p])for(z=9;z--;)q=3&(r=time(0)
+r*57)/7,q=q?q-1?q-2?1-p%79?-1:0:p%79-77?1:0:p158?-79:0,q?!a[p+q*2
]?a[p+=a[p+=q]=q]=q:0:0;for(;q++-1817;)printf(q%79?"%c":"%c\\n"," #"[!a[q-1]]);}
Given a cmos fpga running at 3.3 volts Vccio, the unloaded logic will swing to microvolts of either rail. Do you really think that a visible led couldn't be used to reliably bias the other side of the opamps, to anywhere between, say, 0.1 and 3.2 volts? Why would tempco matter?
You are letting your emotions shut down your ability to think, just because you need to find fault with everything I say. That's very bad engineering.
Checking our stock records, it looks like LM358 (daul opamp) and LM393 (comparator) both cost us about 15 cents, duals in SO-8. Our placement and inspection costs are high, so eliminating the pullups would be a good deal for us. But we don't worry much about pennies of parts cost; usually there's a bigger picture.
We seldom buy quads, because duals take up about the same space but are a lot more flexible. The op wanted 6 channels, I think.
Of course I'm part of it. I work with all my engineers, and we brainstorm circuits all the time... every day in fact; it's a sport, actually. I think the fast opamp level shifter, and the overall pulser architecture, came out of such a session, and I can't remember whose idea it was. In a proper brainstorm session, you never really know, and you don't keep score: the ideas are enough. I certainly didn't do the detailed circuit design on this one... I let other people have fun, too.
IIRC, you can do it with a Si diode drop *if* you also have a series resistor after the diode-- something like 10K, again IIRC.
Best regards, Spehro Pefhany
--
"it\'s the network..." "The Journey is the reward"
speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
A microcontroller would be a natural for something like that. Maybe it's time to try your hand. You could get much better timing accuracy as well.
Best regards, Spehro Pefhany
--
"it\'s the network..." "The Journey is the reward"
speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
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