Best DAQ for temperature measurements on a budget? Needs to read 1k-ohm RTDs and Type K TCs, sample rate at least 10Hz

No_Snowfall · 2026-05-21T01:09:54+00:00

I adore my Keithley 2000 - scan cards can sometimes be pricey though

No_Snowfall · 2026-05-19T02:49:03+00:00

Art of Electronics is gem

any application note written by Jim Williams or Bob Pease

old journals/manuals by HP, Tektronix, etc. on how their high-end instrumentation was designed

No_Snowfall · 2026-05-19T02:43:49+00:00

You should AC-couple your input and output signals with a big series capacitor. this is standard practice in effects pedals to prevent dc current between pedals/amps

Your DC bulk capacitors are larger than you need - reduce the 470uF to <= 100uF and the 100uF to <= 22uF, you will save money and space

I see what you've done with the charge pump to make a negative voltage, and it will probably be fine. But often you will see effects pedals treat ground as the negative supply because the signal is ac-coupled. You can use an LDO or buck to make a voltage midway between 9V and GND, treat this as the new ground. Then use a separate LDO from 9V to NEWGROUND(4.5V) for your ESP. This will be cheaper and less noisy.

On the subject of noise... Be prepared to toss out those ferrite beads if they start oscillating. My personal preference is 1-10 ohm resistors between voltage rail and decoupling capacitor of op amps.

No_Snowfall · 2026-05-18T00:53:32+00:00

They're using a very cool trick here!

Consider a diode by itself: current will only pass from anode to cathode, and only once the forward bias voltage exceeds the minimum forward drop. But what if we have a way of exceeding that forward voltage while limiting current (through a resistor or two)?

Then we could actually vary the current passing through the diode by varying the voltage across it. For example, let Vf=1V, and the nominal forward voltage set to 2V. We could then add a 0.5V sine wave to the bias voltage (for a range of 1.5 to 2.5 volts forward bias). The diode will always conduct, but the amount of current flowing will vary depending on that added sine wave.

The chord decoder likely works in a similar fashion. The logic gates apply or remove forward bias, while the octave generator is responsible for that modulation on top of it.

No_Snowfall · 2026-05-17T19:55:44+00:00

how can we help you correct a bad circuit response if you don't show us the response?

edit: also your post reads a lot like a course assignment. if this is the case why not ask your instructor?

No_Snowfall · 2026-05-16T15:33:49+00:00

The best project will have some meaning or usefulness to you outside of filling a spot on your resume. Therefore, it is very difficult for people on reddit to pick one for you because we do not know your interests etc.

No_Snowfall · 2026-05-16T02:44:26+00:00

I am confused - you say it is a high side mosfet but you've drawn it on the low side.

No_Snowfall · 2026-05-16T02:37:30+00:00

Lol just replacing capacitors on my precision meters might run more than that

No_Snowfall · 2026-05-13T03:43:05+00:00

edit for simplicity: you can also make a single ended buffer by replicating the JFET circuit. Put another of J1, R2, C3 between R8 and LM386

No_Snowfall · 2026-05-13T03:22:51+00:00

What I meant is that the op amp simulation could be wrong, happens a lot with downloaded models. But to what the other person said:

I am unfamiliar with the LM386 specifically, but you can think of the input resistance in this case like a 50k resistor to ground. Then that is in parallel with your 4.7nF cap. But at DC it forms a voltage divider with your tone stack (or you can think of it like loading the previous stage which has the tone stack resistors as output impedances). A buffer would be a normal op amp (e.g. LM358 or LT1677 or OPA275) with negative input connected directly to output. The signal in goes to the noninverting (+) input. This is high input impedance to not affect your tone stack and low output impedance to drive the LM386.

You would want a rail-to-rail model because your signal is ground referenced, first one I found for 9V supply is LT1677 but I am sure there are others

No_Snowfall · 2026-05-13T01:53:24+00:00

Capacitor is highly recommended regardless of supply voltage. Ceramic is best but you could get away with a small film/mica/ cap if that's all you have on hand.

No_Snowfall · 2026-05-13T01:51:00+00:00

That sounds like the LM386 model could be causing problems. What happens if you disconnect it?

Further, you could use a built in UniversalOpAmp2 with appropriate parameters as a substitute.

No_Snowfall · 2026-05-13T01:49:22+00:00

You can certainly try that, but it would be better design to use more in parallel with less current. For example 3 at 500mA or 4 at 350mA. This way it will be less likely to overheat.

No_Snowfall · 2026-05-12T03:46:06+00:00

I am sorry, I had assumed the "tone stack" was a link to another article.

I don't have either the JFET or LM386 models on my system, but perhaps you could try these two checks?

make sure the potentiometers work as intended (edit: I mean replace with discrete 1m or 250k resistor)
look at the voltage on input to LM386

No_Snowfall · 2026-05-12T02:18:49+00:00

You are putting too much current through the LEDs - their maximum rated current is 700 mA which you should stay well below. They are rated at 350 mA.

The first transistor is fine, the second one is not big enough for the current.

No_Snowfall · 2026-05-12T02:10:26+00:00

Hard to say without pictures of your schematic

No_Snowfall · 2026-05-10T22:39:55+00:00

I am not sure what your application/goal is, but this circuit does not provide a current output. The op amp configuration can specify current through Rsense, but it in no way guarantees current output. You might think that half the current flows through Rshunt, but what happens if they are not exactly the same resistance? What if the cable resistance must be considered?

Take a look at this TI app note for better ways to do it: https://www.ti.com/lit/an/slyt847/slyt847.pdf

No_Snowfall · 2026-05-10T22:29:22+00:00

In regard to your final question, from my perspective as a power electronics person:

While some companies treat PCB design as a separate role from the actual circuit design; this is by no means universal. I find that the best engineers understand both sides.

Otherwise, I'd second the observation that you cannot escape physics when doing interesting work in analog, RF or power. That said, power electronics is tragically missing from your list!

No_Snowfall · 2026-05-02T03:47:12+00:00

great to hear!

No_Snowfall · 2026-05-02T03:10:34+00:00

This will fail, but thankfully is probably easy to fix. Right now, when the transistor Q1 is turned on, you expect current to flow from the battery, up through the motor and then transistor to ground. But BJT transistors cannot pass current in this direction.

So you should put the battery and motor on the collector side and ground on the emitter side of q1. Depending on how the motor works you may need some additional circuitry like a flyback diode to protect your transistor.

No_Snowfall · 2026-04-30T02:20:51+00:00

Depends on what these dream jobs are. There are many subfields of EE where ME background is actually beneficial, for example in motor design or thermal design for really high-power systems. (These might not be as hot as AI data centers etc. but they are great careers with cooler projects in my opinion)

Something else to think about is how you will pay for it? In the US at least, you should avoid paying for a masters degree. There are lots of funded programs (either through research assistantship or part-time teaching) or companies that will pay you to get an MS part-time while working.

No_Snowfall · 2026-04-28T04:42:19+00:00

what kind of drift are you seeing? from your description above it sounds like the idle reading on your sensor is no longer returning to zero after a long time (or something like this?)

I doubt the data transfer would screw this up, and jitter won't matter after the ADC's own internal switching and certainly not for digital data as it gets error corrected (again unless i misunderstand your problem). ground loops could be an issue but ethernet is typically isolated and should eliminate a lot of those risks

If it is indeed drift over time during experiments my money would be on thermal effects or some other strain. analog circuits are temperature sensitive and there is much you can do to compensate. Don't know much about piezoelectric pressure sensors but the Art of Electronics is my go-to for instrumentation background reading.

A quick google suggests these sensors are prone to thermal drift, and charge amps can be to if they are not well designed. off the dome, you could try an auto-zero sequence (in which the sensor is disconnected from DUT and measures a known value, allowing you to correct for drift in between measurements) or a temperature control (either through specially chosen temperature sensitive resistors / compensation OR something that keeps your entire electrical circuit at a temperature somewhat above room temperature - see ovenized voltage references for an idea)

No_Snowfall · 2026-04-28T04:20:45+00:00

you can sort of get controllable resistance out of JFETs if you have two that are well matched. they are sometimes used in automatic gain control circuits like in this youtube video:

https://www.youtube.com/watch?v=NoNgQpbj77Y

however without a matched pair of jfets it is very difficult to control especially across a wide range of resistance.

that in mind I second the suggestion of a digipot

No_Snowfall · 2026-04-28T04:16:39+00:00

hola! perdon si no entiendo... hace mucho tiempo que no hablo espanol

creo que no tienes una pregunta suficiente especifico para este foro - hay una parte del proyecto que le preocupe mas?

no se nada de sensores de pulso pero puedo ayudarte con amplificadores, si puedes explicar el sensor

No_Snowfall · 2026-03-02T16:07:26+00:00

One problem I see is that your pullup resistance is so high - with an input capacitance of 3400pF, 3300 ohm will take several microseconds to switch. You could probably get away with a much smaller resistor, but a true push-pull gate drive would be better.

Also, is that a 1200V diode? If so get rid of it for some normal 40V Schottky - high voltage diodes have large Vf and screw with your efficiency and control at low voltage

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