Transforming a signal shape? - Page 1
Forum section: electronics / beginners

author: sgt_johnny
author_rank: Contributor
timestamp: July 15, 2018, 06:11:13 pm
content: Hello Everyone!My question is about transforming a signal shape to another shape:The given signal looks like the following:The normal level is zero volts, in the event of a signal, the voltage rapidly drops (almost instantly) and then slowly coming up to just over zero and then normalizing to zero volts. Basically like a negavite saw-tooht but one side raplidly droping and the other side slowly rising up. Also the signal is very short in time. Because of shape and lenght, the signal cannot be used. A slow ADC would just miss the signal beween its conversion shots, or get a point just anywhere on the signal. For a usefull measure, the ADC should get at least 8 points on the signal.I'm looking for a way to transfrom the signal into either a nice looking positive sine pulse, or better a trapezoidal shape. The lenght (time) of the signal should also be made longer.There is no need for a "out of the box"-Solution, thats why the parameters/voltages of the signal are not relevant, i just want help on the topic, like getting knowledge how the signal can be controlled. Can someone here help me with this topic?Thanks,Johnny

author: tggzzz
author_rank: Super Contributor
timestamp: July 15, 2018, 06:49:18 pm
content: Draw a picture of the required inputs and outputs, showing time and voltage limits.Tell us your problem/goal, as well your solution. In most walks of life, technical or non-technical, if we know the reason for the question you will probably get a better answer. Either the answer will be more pertinent to your needs, or perhaps it can suggest a better alternative that you haven’t even considered. Don’t ask “Can you give me a lift into town?” Do ask “Can you give me a lift into town, so I can replace my broken frobnitz?”. The answer might be “There’s a spare frobnitz in the attic”, thus saving time, money, the environment – as well as making some space in the attic.

author: jeroen79
author_rank: Frequent Contributor
timestamp: July 15, 2018, 07:26:23 pm
content: Seconded.If we don't know what you want to accomplish and what this signal is the we can come up with all kinds of 'solutions' that may not help you at all.

author: Benta
author_rank: Super Contributor
timestamp: July 15, 2018, 07:34:56 pm
content: "Can someone here help me with this topic?"No. As long as we have no idea whether you're talking uV, mV, V, kV or s, ms, us, ns or ps or whatever, there is no way we can help you. A "one size fits all" solution does not exist.

author: David Hess
author_rank: Super Contributor
timestamp: July 15, 2018, 08:18:53 pm
content: If you integrate the signal in the analog domain, then a slow ADC can recover the area. Peak detection can recover the maximum value for a slow ADC.

author: sgt_johnny
author_rank: Contributor
timestamp: July 16, 2018, 07:19:48 am
content: Hi, sorry that i have not provided enough details.I've drawed the signal on paper, see attached. The signal on top is the source, the bottom one is the one i would like to get. Please note that the time and voltage are not "final" and can be different. I would like to get knowledge on how to process the signal, like advises for "if you use this circuit, the signal will come out shaped like ...". Sorry if i provided to few details, i was worried i that i would get a "use this circuit" answer, without proper explanation on how it works.Hope this helps!Thanks

author: Ian.M
author_rank: Super Contributor
timestamp: July 16, 2018, 09:11:19 am
content: You are never going to get the second signal from the first without a time machine as you have drawn it with its leading edge starting before the first!However, pedantry aside, what parameters of the second signal do you intend to measure, and how should they correlate with the parameters of the first signal?

author: sgt_johnny
author_rank: Contributor
timestamp: July 16, 2018, 11:06:51 am
content: Sorry, it is a hand drawing, the signal should start with the first oneI want to have the signal stretched in time, so a slow adc (100ksps) can get much of the signal to measure it. The short singal is not very suitable for measuring. As far is i know ADC like more sine shaped inputs. The signal level should translate in some factor, like -5V on the input will output +500mV on the output. The factor does not have to be a specific one, it only must be the same linearity than the input, the absolute value is not relevant, since the adc will always measure a deviation from "zero". A calibration will be done only from ADC values, the true voltage levels are irrelevant.I discovered a product which actually does something similar to my problem:https://www.fastcomtec.com/fileadmin/user_upload/cr200_04.jpgBut i would really like to know what circuitry is inside this modules!

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 16, 2018, 11:32:11 am
content: If it's always the same voltage and time, why does it need to be read by ADC? Use a comparator and latch to generate a trigger. The pulse is probably enough that it can be fed (via coupling capacitor to address the voltage offset) to a microcontroller's timer capture pin, and you can measure its timing there.Tim

author: sgt_johnny
author_rank: Contributor
timestamp: July 16, 2018, 12:39:32 pm
content: No, the signal level matters, but it doesnt have to be a fixed, known factor of the input. As long as the output has the same linearity than the input, i'll be fine. The ADC hast to measure the peak of the signal, thats the value i like to know.

author: Ian.M
author_rank: Super Contributor
timestamp: July 16, 2018, 02:15:24 pm
content: If the source is low impedance and you don't care if you loose small pulses (say less than 1V peak), this (LTspice sim) should work. The OPAMP + supply needs to be greater than the max possible peak pulse voltage. The MCU must provide a control signal to reset the voltage on the capacitor after the ADC has measured it.