What are some techniques for filtering and amplifying pulse signals?

[petterg]

I'm on a new approach to this. What I have now is two outputs, one in the range Pp=[0;2]V, the other in the range Pn=[-2;0]V. If abs(Pp) > abs(Pn) the pulse is positive, if If abs(Pp) < abs(Pn) the pulse is negative. If abs(Pp)+abs(Pn) < X the signal is too weak to be considered valid.

I haven't decided on the value of X yet, but the plan is to build the validity check by connecting Pn to an opamps negative input, Pp to the positive input, and tune gain so that a diode on the output will give signal only if signal is valid.

The new challenge: How to make a comparator for the absolute values? I'm thinking the output of the comparator could be +2.5V if Pp is the larger, or -2.5V is Pn is the larger.

 

[meBigGuy]

I think I would use a second comparator for Pp-Pn > X where X is set by a pot, or maybe even dynamically. You need an amp to create Pp-Pn, which you may also want to condition. I wouldn't try to gather so many functions into one amp.

 

[petterg]

Into one? I'm trying to not exceed 2 quad.
Attached is sketch of the comparator. Basically it compares both inputs to vgnd, lowpass filter and summarize. It works quite well. If signal becomes too weak it starts oscillating the output, hence I don't need a validity signal. However, if signal becomes too strong it gives a random output... But here is a workaround: I theory the signal will never reach the strongest level on one of the sides. If that turns out to be real signal may be compared to some voltage a little bit off vgnd.

I'll let this project rest until the high power resistors arrive so I can power up the sending circuit. According to schedule they'll arrive on Wednesday. (And I might not be traveling next week)

 

[jim hardy]

I've hung back - felt I was confusing more than helping, plus got busy with some pressing projects.

I thought you were close with your filters

What does this thing do? Are you building a communication system, or trying to decode some existing signal?

Frequency modulation/demodulation is mighty easy with IC's of the 1980's,

AD630 datasheet shows examples of picking signal out of noise with synchronous detection

and amateur radio buffs have used frequency shift keying for over fifty years

 

[petterg]

Just that I don't understand all your cleaver ideas doesn't mean your confusing :)

Removing noise turned out ok. Removing that drifting offset never really worked out without destroying the signal. My new approach is positive and negative peak detection then comparing the peak levels. It seems to be working as long as at least one of the peak detectors doesn't clip. Also there's some rippel on the peak detectors output. When signal is weak this rippel can make the output level of the two peak detectors to cross, which makes the comparators output oscillate. I think it is working within the voltage range needed.

The circuit is supposed to signal to a mpu if the received signal is the sent signal, or the inverted. (Or no (too weak) signal.) Signal is not modulated, all thou I've been looking into modulations thinking that it might come handy. Phase shift modulation of a pulse train seemed to be the most suitable. That phase shifts 180 degrees every time there is a transaction from 0 to 1 or 1 to 0 is easy to understand. But how do the receiver know, when powered on, if the current signal caries a 0 or a 1?

Attached is the sketch of my retriggerabel dual 555 with triggerblock. One of the 555's is (re)triggered continuously while input is higher than about 2*Vcc/3, the other is (re)triggered when input is lower than about Vcc/3. While the output of one 555 is high, the other is blocked from triggering. It might be useful if anyone else need something similar from a 555.