That applies to voltage sensing circuits too. Once you know the current resistance of the thermistor, either by timing or measuring the voltage of a potential divider, you then should look up the thermistor curve to find out the temperature. Although as you say it may be linear enough for part of the range.
Theo
Yes, though the Pi doesn't have any schmitt trigger inputs on its GPIOs.
The closest that you get to specs for these this with the chips used in the Pis are the datasheets for the Compute modules that use the same SoC. Even then I wouldn't trust those specs blindly.
CMOS inputs also aren't meant to linger in the "intermediate zone" between LOW (under 1/3 supply voltage = 1.1V @ 3.3V supply) and HIGH (over 2/3 supply voltage = 2.2V). If they do then there is potential for any variety of undesireable and unpredictable behaviours. What you need in this case is an external Op-Amp chip configured as a comparator, which will do the level detection of the analogue signal and produce an output which can be compatible with the Pi's GPIO (if you make sure that the LOW and HIGH voltages fall within the ranges above, and that the signal can never go higher than the Pi's 3.3V supply).
-- __ __ #_ < |\| |< _#
Not even that. it will in fact hover between states drawing lots of current if its normal CMOS. You can make a crude analogue amplifier out of a CMOS inverter.
-- "I am inclined to tell the truth and dislike people who lie consistently. This makes me unfit for the company of people of a Left persuasion, and all women"
IS the PI GPIO input schmitt trigger?
-- There?s a mighty big difference between good, sound reasons and reasons that sound good. Burton Hillis (William Vaughn, American columnist)
On a sunny day (Fri, 28 Feb 2020 22:38:54 +0000 (GMT)) it happened "Dave Liquorice" wrote in :
An other effect that may happen on a slow rising (or falling) edge is oscillations, usually a minimum rise-time is specified for analog inputs. A thermistor would not be fast as we talk about nano seconds here. With a large capacitor at the input like an other poster showed in his solution chances of oscillations happening ere likely zero.
Schmitt-trigger inputs will not normally oscillate but flip state and stay there unit the input is a lot changed the other way, but will be an oscillator when you add a capacitor :-)
I used a i2c ADC chip from Philips PCF8591 as 4 channel analog input and 1 channel analog output on the parport of my old PCs in the eighties. Probably have some old C driver code for it around somewhere. Else these days Linux should have support for it as I see it in /usr/src/linux/drivers/i2c/chips/pcf8591.c
I wrote
eeeeh DIGITAL inputs..
On the last statement: I can confirm that a CMOS inverter does make a pretty decent analog amplifier for some purposes. In the latter 1970s, while a freshman studying EE, I used CMOS part number 4449 inverters (balanced current drive) as analog gain elements for an integrated stereo amplifier. I think it was an article in Popular Electronics that gave me the idea. IIRC, the article showed that unity gain was around 1 MHz with a 15V power supply. For audio purposes, the inverters worked very well.
The basic idea is to use DC negative feedback to bias the inverter at the crossover point where the input and output voltages are the same. For audio purposes, it works best to use split power supplies, +5V and -5V up to +5.7V and -7.5V. You want the power supplies to be pretty clean, because power supply noise rejection is not spectacular. You use capacitive coupling between stages to keep stages isolated from each other in DC terms. If you want controlled gain, use a series resistor on the input side to make the inverter's input a virtual ground. For audio frequencies with +7.5 and -7.5 power supplies, 10X voltage gain (20dB) works well, with the feedback resistor being 10X the value of the series input resistor.
If you need more gain than you can get with one inverter, do _NOT_ chain three inverters end-to-end and put your feedback loop around the chain. I found out later that configuration is called a ring oscillator. What I had intended to be a phono input stage with RIAA equalization turned into a rather strong oscillator, probably roughly square wave at somewhere in the neighborhood of
200kHz.The CMOS inverters served well for a few years until I learned about and could afford BiFET op amps. I redesigned the whole thing with BiFET op amps, and that unit is playing music in the living room as I type this.
-- Robert Riches spamtrap42@jacob21819.net (Yes, that is one of my email addresses.)
On a sunny day (1 Mar 2020 00:57:14 GMT) it happened Robert Riches wrote in :
Yes it works, been there done that, but it is no HiFi etc etc, avoid it!
In those days the LM380 was a much better choice, real power amp, just got a bunch from ebay a few month ago, still available
The issue of using logic gates with half-way input voltage may indeed cause excessive power consumption.
Bifet is not bad but there exists today an opamp that is low enough noise to match the very best discrete circuit that I used to design back in the 70s .
I think unity gain on CMOS is a lot more than 1Mhz tho.
-- "When a true genius appears in the world, you may know him by this sign, that the dunces are all in confederacy against him." Jonathan Swift.
On a sunny day (Sun, 1 Mar 2020 08:56:41 +0000) it happened The Natural Philosopher wrote in :
Oh, sure I am not uptodate on what the latest and greatest is (ask in sci.electronics.design if you need to know) but bought a few TCL274 quad opamps a few month ago as sort of universal opamp for projects, specs:
VDD = 5 V
Wide Range of Supply Voltages Over Specified Temperature Range:
Single-Supply Operation Common-Mode Input Voltage Range Extends Below the Negative Rail (C-Suffix and I-Suffix Versions) Low Noise . . . Typically 25 nV/Hz at f = 1 kHz Output Voltage Range Includes Negative Rail High Input Impedance . . . 10^12 Ohm Typ ESD-Protection Circuitry Designed-In Latch-Up Immunity desription
Much better than the LM324 :-)
Oh yes, and there is, after the CD4000 series, the 74HC4000 series.
The TCL274 has a gain of 1 at about 1 MHz, but I typicaly use these things for measurement equipment design. Not done much audio lately, apart from funny little things like this:
Try the LM833.
At typical phono cartridge/MC microphone source impedances, that's around 4nV per root hertz
Noise performance of Bifets like TL074 only beats that when running from very high source impedances.
I used to try and get close to 2nV/root Hertz when designing phono inputs.
-- "When one man dies it's a tragedy. When thousands die it's statistics." Josef Stalin
On a sunny day (Sun, 1 Mar 2020 10:11:02 +0000) it happened The Natural Philosopher wrote in :
Looks nice, real audiophile opamp:-)
Very impressive long before that on my old Garrard turntable with Shure element you would hear all sorts of motion related artifacts.
Digital is nice... there is a lot of good compression software too for Linux: lame, and players like mpg123. And of course things for the wave format. Multi-channel wave was once part of a project I did, for multiple languages simultaneous translation, that resulted among other things in multimux for Linux, some of that old stuff is here:
I have xpequ running on the P4 and col_pic too:
Getting carried away here, audio IS an interesting subject ;-)
I've used the DS13B20 in many applications with parasitic power.
ONE WIRE (plus ground). One. Uno. Hitotsu. Ein. Un. It works.
As I recall, you use a 2k resistor between 3.3v and the data line, and connect data and ground to the correct GPIO and ground on the RPi. The
1-wire interface should be able to handle devices that use parasitic power.but if you want to split hairs over terms, *whatever*... (most people find nit-pickers to be irritating)
-- (aka 'Bombastic Bob' in case you wondered) 'Feeling with my fingers, and thinking with my brain' - me 'your story is so touching, but it sounds just like a lie' "Straighten up and fly right"
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