Hello everyone, first post from a long time Lurker.

I have a project I have been working on where I'm using an ultrasonic signal to to stop a robot/buggy from hitting an obstacle. My circuit is designed so that when there is no signal, my relay is not activated and the motor circuit has current flowing to it, and when the circuit detects a signal the circuit amplifies the signal and then triggers the Relay.

As I have said I am having issues triggering the relay, specifically the relay as you would imagine is switching on and off as the signal is processed by the circuit. I ideally would like the relay to be active during the time the signal is being received. But currently I have no Idea how to go about this, for a period thought a 555 missing pulse counter might do the trick, but no (it sort of does but gives me the same issue I'm stuck with now). I also tried using a LM567 tone decoder, but alas Proteus doesn't have a model of it so I cant simulate it.

Here is what I have currently,

http://i.imgur.com/1ZapI.png

In this instance all there is is a 40kHz Square wave being generated, mainly because there isn't a transducer model in Proteus and I'm using a 555timer as an astable multivibrating ultrasonic generator. The circuit is inactive as I have the button switch open to simulate there being no obstacle.

http://i.imgur.com/koith.png

Here's is the circuit with the signal flowing through the circuit. The RC filter is designed for 40kHz, I then put it through the op-amp and filter it again. In the above pic I have the last opamp operating as a comparitor, but it switches on and off with the peaks and troughs of the signal, so in turn it switches the relay on and off.

Genuinely I am lost, I can see ways of doing it in my head but I can't move from conceptually in my brain to conceptually in a simulator. I'm pretty sure I can get the missing pulse generator to work if I can rectify the signal (in the above pic its the green signal) but for the life of me I'm lost on how to do it.

Can anyone help me, any type of help, where I am going wrong, what I could focus on, am I even using the right type of triggering circuit. Honestly anything would help I am at my whits end.

Here is my circuit with the missing pulse detector, if any of you are interested.

http://i.imgur.com/or8mv.png

Anyway thanks in advance, I think talking/typing through has helped a little allowed me to think at what I'm am trying to achieve (if that makes sense).

TheFrin

 

I think the first step would be to determine what exactly will be the signal you will get from the US transducer under different conditions.

What sensor are you planning to use? A range finder?

It's relatively easy with the $6 range finders you find on ebay.

If you plan to develop the whole transducer part as well it is going to be different. The received signal will not "be there" or "not be there". You will get back a signal of changing amplitudes, so you have to determine the threshold yourself.

(The range finder I was talking about already do the threshold part for you)

 

I think the first step would be to determine what exactly will be the signal you will get from the US transducer under different conditions.

What sensor are you planning to use? A range finder?

It's relatively easy with the $6 range finders you find on ebay.

If you plan to develop the whole transducer part as well it is going to be different. The received signal will not "be there" or "not be there". You will get back a signal of changing amplitudes, so you have to determine the threshold yourself.

(The range finder I was talking about already do the threshold part for you)

Thanks, I needed some guidance, simply put, I will know the signal tomorrow, I am going to build the signal generator and run the receiver transducer through an oscilloscope and see what I get.

Essentially yeah I guess it is a range finder, I want my little robot to stop about 100mm from an obstacle, I also want to build it myself practice my breadboard and soldering skills.

How would I determine the threshold?

Aghhh I was planning on going to bed hahaha yo have me thinking again. Thanks for the comment though I have even more half formed thoughts.

TheFrin

 

How would I determine the threshold?

I really think you need to know first what you get from your transducer.

Even with a range finder module you will still have to do some work ...

I bought this one recently. Works fine. http://www.ebay.com/itm/Arduino-Ult...129?pt=LH_DefaultDomain_0&hash=item231a00fa99

 

Or, one better, carefully define your problem and then figure out the solution. I'd avoid relays at all costs, myself. MOSFETs and things are more efficient a lot of the time.