@JonRB oh! Voltage at the output is also Vcc2 (looking at 9.3.1 on the data sheet). Current flows from Vcc2 to Output, but the load amperage is contingent on ohm's law.

@W5VO Hey, we were chatting about my project yesterday night (not sure if you remember). I was having trouble using high impedance force sensors since I was getting some noise in my circuit. I have since rebuilt it up (but only the single op amp circuit and using a single resistor instead of a digital pot). Here is what the circuit looks like:

@user2899444 Thats the one :) give or take additional strays its basically the supply/R_load

For steady-state

@W5VO here is an oscilloscope shot with an unloaded sensor

under PWM with an inductive load it starts getting... mathy

@W5VO So from my calculations, I used a 0.01uF cap to filter out 60Hz noise.

but you didn't have 60Hz noise

but I am still seeing quite a bit of noise in my signal :(. I have a bypass cap on my power supply as well

@W5VO i was doing research and others said to add a filter for 60Hz noise for AC signals

why not make it so that the 60Hz doesn't get onto the sensitive section

rather than Filter like that

@JonRB Thank you so much! It seems like the 'absolute maximum current' rating that both transistors can handle (datasheet 9.3.1) is 1 amp continuous but 2 amps would be at critical levels.

@JonRB So I would have to be careful not to have over 1A specifically to the output pins, correct?

yup

among other conciderations.

ok! Thank you so much!

Does anyone have ideas for the issue I am having. I really need some guidance. I am just stuck and would love some help.

Its a simple circuit (I cut out 95% of it), so I hope that helps in solving the problem

thanks in advance!

@ta

@tabchas you need to treat it as a differential signal to cancel out the pickup.

@JonRB How can I cancel out the pickup? I'm guessing I need another filter?

no...

treat the incoming high-impedance, low-amplitude, force-sensor ... as differential

the pickup should be commonmode

sounds like bad setup w.r.t. the sensor...

@JonRB ok, so I would need extra hardware to read in the differential signal right? Since an Arduino's chip does not support differential signals. Sorry if I don't fully understand, I'm trying to read up and understand what you mean.

well you need extra hardware if you want to filter that "noise" so why not do it properly and eliminate it

@JonRB got it. its just weird since these were supposed to be out of the box sensors and they are just giving a really bad signal output with the recommended circuit

They never state the conditions

equally you might be doing some silly things with ur setup....

@JonRB thats what I think I am

@JonRB I just don't know what :(

need a photo of your setup really.

@JonRB 2 mins, and thanks!

not doing much :) just some CS:GO as I can't sleep and REALLY do not want to start simulink for work,·..

@JonRB haha nice :)

ignore the green board in the middle. its not connected to anything

where is the sensor?

its the wires protruding out the image

or are you just using a voltage divider at the moment.

the two red wires

right

for starters they should be twisted

no, its not just a voltage divider circuit

heres the circuit: i.sstatic.net/ISdHA.png

I had twisted the wires, and I got new ones just to make sure that wasnt causing anything :(

but those are pretty short

likewise, while you are trying to 0V/EARTH/GND reference the divider... the return should be close to the OPAMP not at a 0V/EARTH/GND.

What you have has quite a nice loop for ... pickup

where is the OPAMP decoupling capacitor?

theres a decoupling cap on the power rail

and that supplies the op amp

but how far away is that capacitor?

where is that 5V generated?

the black and red wires at the top of the power rail go to my Arduino

do you have any form of common mode choke to block crud coming onto this setup

what do you mean by common mode choke?

stops crud

no, don't have a choke

urr ok...

personally I would have setup a PI filter from the arduino to this "sensor circuit" (if the arduino is the source of the power)

Keeping the rail clean and the 0V as clean as possible

decouple the OPAMP as close to the IC as possible

the sensor/resisistor to have a twisted pair leads to reduce the loop area for pickup

you are after a x1.082 gain and are using some quite high value resistors so they will be quite ... noisy

why not use a diff amp?

or if you are concerned about input impedance... an instrumentation amp?

@JonRB This op amp was recommended by the manufacturer of the sensor, so I thought it would be the best to use

do you have a link?

@JonRB yes sir - tekscan.com/products-solutions/force-sensors/a301

@JonRB also this:

which is exactly how I have mine setup

I would consider the layout.

?

@JonRB I wanted to confirm my understanding on something. You had mentioned PWM frequency and inductance. I figure I find the inductance of the electromagnet but the PWM frequency is determined by f = 1/(2*pi(LC)^0.5), correct?

@JonRB here's a much better pic of my circuit setup. This has no decoupling caps on it as yet.

morning

This old post made my day - electronics.stackexchange.com/questions/29969/…

@Whiskeyjack Every once in a while someone wants to build her own PC motherboard.

so...when laying out a real-time clock on a four-layer PCB with the global ground plane directly under the layer the crystal traces are on, should you do anything to the ground plane under the crystal and its traces?

@Shalvenay That would make a pretty good question for the main board. Especially so, if you add a link to the datasheet of your RTC (or the MCU, if the RTC is a part of an MCU).