triangle

The theory was that they were bought as a last ditch effort to stay in school. Didn't work. It was a really dumb plan to take that particular course if you were on the bubble, too.

The best calculator ever. Someone lifted mine. Apparently your wife had the same problem. ;-)

Not sure what they taught in Linear Circuits but at our university hardware classes were boring because I knew most of the stuff from ham radio. So I mostly didn't attend, there was no requirement to. You just had to pass the exams, sometimes grueling ones.

Let's say she invested it. Looking at her walk-in closet there was a very good ROI.

We've got tubes of the ICL8038's if anyone wants some.

JL, why not a 555?

George H.

It was a lab course, so attendance was rather mandatory. It was a summer semester (8 week semester), so rather intense.

You're married to Amelda Marcos, too? ;-)

Reverse Polish is good for your brain.

I attended community college using veterans benefits (GI bill). I had attended military electronics schools, so I had a head start and got good grades. We had one older student (age 38) in a AC circuit analysis class, who owned one of the first calculators. That was in 1971 so it might have been been a SR-10 or 11. The instructor was constantly asking him to work out problems. I bought my first calculator (HP-21) in 1975 used for $200. I recently bought a HP-25 programmable calculator at a swap meet for $3 including manuals and it works fine. And my neighbor gave me a HP-28S calculator with a LCD display and much more capability, but the key construction is not as good as the old HP-21 or 25. The HP-28s has a whole row of keys (5) that don't work. Probably one bad connection that wipes out the whole row, but I don't want to take it apart, since it might not work again. The old HP-21 never fails.

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What is wrong with one of these?

I've got an older, smaller one that should do nicely. If you don't need the 10k and 100k ranges it seems to be 100%. The sine waveforms on the higher two ranges are wonky. Sounds like you want a slower ramp so it should be fine. I'll sell you mine for $50. I'll throw in free shipping, lol.

Aside from my moral repulsion for 555s, I need precise upper and lower voltage swing points so I can sweep the ADC codes. And linear sweeps would be nice. With a linear triangle, every ADC bit should have a 50% probability. Stuck bits, or bits shorted to other bits, will mess up the statistics.

The exponentials of the 555 are ugly and harder to think about, and level shifting would add parts.

Your circuit is pretty much a 555 + external intagrator.

But he wants close control over the max and min of the ramp. The 555 is always at 1/3 and 2/3 of Vcc. It would be a bit of work to give the 555 the inputs it needs to do that.

Gonna be hard to do when you don't even list a pn for the comparator on the diagram.

That's right, and the 555 comparators do not match his analog requirements.

When exam answers assuming pi^2=10 and g=10 were perfectly acceptable, my university deliberately set a question for first years where it was necessary to use a calculator (show the voltages at nodes in an inverting opamp amplifier).

Most people fell into the trap; the better ones didn't.

Why not toss in a LM393 and CD4013, same supply for all parts? It's not like it needs to be fast or low power. Then you don't need the -5V ref and oddball resistor divider on the left. And the slower risetime will ease the peaks. 'HC (or worse) will definitely lead to nippling.

Tim

Yikes, 50 dB CMRR guaranteed. Move the input by a volt and the offset changes by 3 mV!

Cheers

Phil Hobbs

Yeah I figured as much. (I was going to add a comment about getting help from someone here. .. but decided that would be too divisive.)

I would have done a 555 or other thing and bodged the output with an opamp for range and offset. (But I'm a brute force type, when it comes to electronics.)

I don't really know, but I thought you can get a triangle out of a 555.

George H.

It is approximately a triangle, but not really. There is some curve to the slope between 1/3 Vdd and 2/3 Vdd due to the RC time constant. That could be a killer in some circumstances. My guess is that JL is trying to achieve the best he can so that it will be one less error to hammer out.

Looks like simple arithmetic to me, this one will have no problem doing -1 to +9. Comparators are fully protected. Dunno why you even have that +12V supply in there, now you have to protect ADC.

Please view in a fixed-width font such as Courier.

. . . . |\ . TRIANGLE >---[15k] --+----+----------+------|-\ . | | | + | >------ . | - | V -|+/ | . [10k] ^1N4148 | TH |/ | . | - | o . | | | P . --- --- | . | . | C . | o . | |\ | . ------|+\ | . - | >------ . V -| / . TH |/ . . . . + . 2.5 x V . / \ TH / \ . / \ / \ . / \ / \ . TRIANGLE / \ / \ . / \ / \ . / \ / \ . / \ / \ . / \ / \ . - . 2.5 x V . TH . . .

As it turned out, it was a waste of resource to give you so much as a No. 2 pencil...