Hello all

I am facing a problem, I have a feed back signal from a sensor that will "travel" by a cable in a noisy 50hz environment.
I am looking for a solution where no microcontroller is involved, well, at least no software involved.
The solution will be integrated on two pcb
My guess is that that the signal will pick up a lot of noise and interference from outside the cable (ordinary flat cable) so therefore i do not want to feed the receiving with my fairly high impedance feed signal side.

My idea was first to use a PWM set but all they all suffer from either high prices for the chips, a lot extra components and a 2 order RC filter on the receiving end, causing long response time and still have ripple.

My second thought was to isuse VCO, Voltage control Osc and a Osc controlled Voltage but they all suffer from high prices for the chips.

So my idea is to connect an ADC directly with an DAC, but i can not find a good solution, I want the ADC to continuous feed the DAC without any control logic involved. (ADC101S021 seems to do the ADC trick, no protocol or i2c/spi commands) just feed it with a clock and it output data)


Is there already a good solution to this problem?
What is the best way to do this ?
Is there any tips of self operating ADC/DAC that can do this?

 

hi Stefan,
What is the specification/parameters of the signal you are planning to TX.
ie: Frequency range, amplitude etc.
Cable length?
E

 

You've left a lot of important things unspecified or extremely vague.

You talk about causing long response time, so presumably response time is important. But what response time do you require?

You talk about a concern over it still having ripple. But what level of ripple is acceptable?

You talk about high prices being a concern, but give no clue as to what kind of budget is acceptable.

You give no indication of what kind of signal this is or how well you need to be able to recover it at the receiving end. Recovering a 100 mV signal with 0.1% accuracy is far different than recovering a 10 V signal with 1% accuracy.

If you go the ADC->ADC route, can you tolerate the latency involved if you can't tolerate the processing of a PWM signal?

Why are you so resistant to using a microcontroller? Simple ones are dirt cheap.

 

What do you mean by "feed back from a senior" ?.
What is the sensor ?
Are you fixed upon the cable ?
And all the above questions .

In general
Differential is better at noise rejection
If single ended , screening is good and watch for the ground return .
If you can amplify the signal at the sender and attenuate it at the receiver , external noise is also attenuated.
Also in general , one can filter the noise if it's outside your band of interest.

 

As above, we do not know anything about your requirements for the signal or signal fidelity. You're direct, A/D-to-D/A approach can work, but you still might need a reconstruction lowpass filter at the D/A output. This depends on the ratio of the A/D clock frequency and the frequency and shape of the analog signal. Without it, there will be "stairstepping" in the output signal. That is a form of distortion caused by the quantizing of the original signal by the A/D.

Cable distance?

ak

 

noisy 50hz environment

How often do you need to sample the data? If you need the data very slowly, then adding a low pass filter to remove noise above 10hz will help. But if you need the data without delay a low pass filter will not work.

Normally I send the analog data and a reference voltage down two different wires. On the receiving end I use a differential receiver that subtracts the two signals. Often the noise will be the same on both wires and will be subtracted out. OR. Send the signal and the inverse of the signal down two twisted wires. The differential receiver will hand you 2X the signal with the noise removed.

 

What type of cable is used for the sensor and how long is it?
If you're dealing with high resistances, the requirements for the cable are even higher.
The cable must have a good quality shield, and the shield is connected only at one end.
In some cases, you have to use a galvanic isolator, but they aren’t cheap.
To give some specific advice, you need to describe the circuit in more detail

 

Another approach is to filter out the 50 Hz noise with a comb filter at the source.

ak

 

Another approach is to filter out the 50 Hz noise with a comb filter at the source.

ak

At the source?

How will that filter out 50 Hz noise picked up in the lines between the source and the receiver?

 

How will that filter out 50 Hz noise picked up in the lines between the source and the receiver?

Put the filter on the receiver end.