Circuit signal delay methods

[WhiteKnight]

I'm designing a circuit that requires a signal delay on the order of about 1s but I'm not sure how to go about implementing it using simple components. Basically, I need the signal to come in to some series of elements that delays the propagation of the signal by a set value. I'm trying to use only simple elements as this circtuit will ultimately be incorporated into a self-replicating robot, so the simpler, the better. Any ideas?

 

[dkozloski]

What type of signal do you want to delay? Analog or digital? It makes a huge difference. If all we're talking is a single pulse at a time you could use a one-shot multivibrator or a time delay relay. If you have some sort of analog signal, you are talking something clumsy like a tape loop. You can delay a digital string with memory and a dump circuit.

 

[blahblah99]

What you could use is an op-amp delay circuit that'll delay the input signal by a time of R*C,

where C and R is the high-pass filter network to the positive input of the opamp, with a unity gain feedback on the negative input.

 

[KilroySmith]

Well, if you were looking for a delay on the order of two and a half seconds, there is a very simple approach. Using a high-power transmitter and high-gain parabolic dish antenna, bounce the signal off a reflector located on the moon (I'm sure there are a few left over from the Apollo days). This will give you a fairly precise (2*(384,400,000 m) / (308000000)) = 2.5 second delay.

If your budget is too tight, you'll have to provide information on the signal that you are trying to delay. Extremely low frequency Analog signals are pretty easy; low-frequency digital is pretty easy. Delaying high-frequency Analog or digital starts to become more difficult.

/frank

 

[WhiteKnight]

It's a 5V analog, DC signal. Basically, I want it to go to the base of a transistor for 1s, then go to ground.

 

[KilroySmith]

Are you trying to create a 1-sec wide pulse in response to some event, or are you trying to take an arbitrary signal, delay each point on the wavefront by a second, and re-output the signal?

 

[blahblah99]

Originally posted by: WhiteKnight
It's a 5V analog, DC signal. Basically, I want it to go to the base of a transistor for 1s, then go to ground.

Feed that 5V signal through an op-amp integrator whose output then gets fed into a comparator. The output of the comparator goes to the base of the transistor, with a pullup resistor of 1k or so. Play around with the integrator values until you get a delay of 1second.

What happens is that 5V signal will get fed into the opamp, which integrates that straight line. The output will a voltage that's increases linearly with time. Feed that into the comparator who's reference voltage is at, lets say for example, 2.5V. Once enough time passes, it will trigger the comparator which will provide a low impedance path to ground at the base of the transistor, which turns it off (assuming that it's an npn or nmos device you're talkinga bout).


However, the transistor will still be on even with 0V due to the way the comparator's configured in this case. The transistor only turns off after 1second when 5V is applied to the input of the integrator.