A few questions about schematic

  1. In one of my design classes, I'm building an ultrasonic radar. I looked online and found a decent schematic for it and I have a question about it. In the schematic I circled two things that I have no clue why they are there. I'm not sure how to connect the Vcc and ground to that part of the nand gate. I have no clue where or how to connect them in my circuit. Can someone explain to me why they are there and how to hook them up?


    Here is the original site

  2. jcsd
  3. i think your getting the symbol of the nand gate confused. pins 7 & 14 don't belong to the input of any of the nand gate but is the power supply for all the gates. just hook pin 14 up Vcc show as the circled 1 and hook pin 7 to ground shown as circle 2.

    it's weird that you would have a problem with the nand chip but don't ask about the op-amps. also what does the darlington npn collector connect to circled pin 9. :confused:
  4. I am wondering about that npn transistor pin too. Anyone know? Or could someone supply me with a better schematic?
    Last edited: Nov 3, 2005
  5. berkeman

    Staff: Mentor

    That's not a very good ultrasonic radar circuit. The Darlington output stage looks like you would hook up some output indicator to it, like an LED or buzzer or something. The output collector of the Darlington probably pulls low when the received US signal varies too much.

    But having the transmitter piezo and the receiver piezo so close together on the same PCB will severely limit the sensitivity of the "radar". A better design would seperate the TX and RX parts of the device, at least by a meter or two. And it seems like it would be better to have two RX units, and compare their outputs to determine if there was movement going on....
  6. Do you have or know of any other designs I could use? Anything at all would be helpful :smile:
  7. berkeman

    Staff: Mentor

    Depends on what you want the "ultrasonic radar" to do. Do you want it for rangefinding, or for motion detection like for an alarm system?
  8. Rangefinding
  9. berkeman

    Staff: Mentor

  10. Is this what I want?


    or maybe this site???


    Edit: Here is the info from my worksheet about this project:

    For this project you will create a radar set using an ultrasonic transmitter/receiver received from the instructor. Radar operates on the principle of sending out a pulse and then timing how long it takes before the echo is received. The longer the time, the further the distance. The initial pulse needs to be fairly fast. The counter also needs to be fast.
    The ultrasonic transmitter/receiver will be mounted on a shaft attached to a stepper motor. The stepper motor needs to be able to sweep across 180 degrees as the radar is transmitting.

    Grade based on, Distance Ranging (25ft), Stepper Sweep (0 to 180deg), Display on Oscope.
    Last edited: Nov 4, 2005
  11. berkeman

    Staff: Mentor

    Yeah, those both look like good learning kits. I especially like how the first one made it a point to improve on the Polaroid rangefinder.

    Since your prof is going to be providing the transducers, will you be allowed to use a canned kit, or do you need to build it from scratch, using the kit as a learning tool to guide your own design? What uC are you supposed to use? Do you have the stepper motor part figured out already?
  12. I'm supposed to basically build it from scratch. My professor gave me the transducers, the stepper motor, and two chips for it. The first chip is the L298 Dual Full-Bridge Driver.

    The other is the L297 Stepper Motor Controller.

    Another person showed me this schematic.

    It's supposed to be for a robot but he said it should work and it looks easier then the previous schematics. Your thoughts?
    Last edited: Nov 4, 2005
  13. berkeman

    Staff: Mentor

    I like the LM567 in the MiniBot schematic. The piezos are probably pretty narrowband, though, so I don't know how much more noise rejection the 567 will give you overall.

    What is the output of the range supposed to be? Are you supposed to use a microcontroller to do the stepper motor control and calculate range versus bearing? How are you supposed to present the information? Do you need a USB connection to a PC to display the data, or are you supposed to drive a small display? Sounds like a fun project. How long do you have to get it done?
  14. What is the output of the range supposed to be?[/e]
    I'm not sure about that.

    Are you supposed to use a microcontroller to do the stepper motor control and calculate range versus bearing?
    I wasn't given any info on that. All I know is that the stepper motor has to sweep 180 degs back and forth.

    How are you supposed to present the information?
    I'm guessing that I'm just supposed to make it sweep the 180 deg and while it is doing that, It should detect objects within it's path.

    Do you need a USB connection to a PC to display the data, or are you supposed to drive a small display?
    My professor never said anything about a USB connection, so most likely the small display, such as a led or a few 7 segment dispays.

    How long do you have to get it done?
    Until the end of the semester, which is around a month and a half.
  15. berkeman

    Staff: Mentor

    Well in that case, you should start experimenting with driving the TX piezo, and see what the best way is to get a short loud wavelet pulse out of it, and start experimenting with input preamp and filtering stages to see what kind of RX sensitivity you can get. Do all this experimenting with an oscilloscope and simple components, and then use those results to guide what you do for the rest. And ask your prof the questions I was asking -- it may be that he's leaving out that part of the assignment to see how creative people get. Like, you might get extra credit if you did use a microcontroller like a PIC that also has a USB port, and you graphed the data real-time with a Tcl or C program on your laptop or something. Maybe even make it look like a real radar display, with the line sweeping through bearing, and blips staying persistant where you are getting echos. Maybe even designate them as targets, with little airplane symbols and friend/foe and ....... oops, sorry about that. Sometimes I get carried away :-)
  16. First of all, what are piezos? :)

    Second, how should I go about putting a 9V and 5V High in the circuit? Do I just use two separate power supplies?
  17. berkeman

    Staff: Mentor

    I can't tell by the smiley if you're kidding or not, so I'll answer about the piezos. Piezoelectric transducers are what is used for the ultrasonic TX and RX elements. A piezoelectric crystal (or sometimes polymer) changes size with an applied voltage. Piezoelectric crystals are used for clock generation (like the 32kHz crystal in your watch, or the 10MHz crystal on many microcontroller boards), and when made big enough, they can be fairly efficient at coupling ultrasonic sound waves into the air. I don't know if your ultrasonic transducers have built-in oscillators or if you need to drive them at their resonant frequency, but it the prof gave you the datasheets, it will talk about how to use them. Come to think of it, start with the part datasheets and see if they have application information on them. Or go to the manufacturer's website and look for application information. They will show you the optimum TX and RX interface circuits.

    And on the power supply question -- initially just use two outputs from a bench supply. Eventually you will need to include a power source and voltage regulators on your final project assembly.

    Also, look around some for application info on whether it's worthwhile to have a directional antenna structure for the RX piezo. Like, even just a few inches of plastic tubing. That will give you better resolution on the bearing of echos.
  18. Why would I have to include a power source and voltage regulators on the final project assembly? Wouldn't it work fine if I just used the 5 Volt line from my power supply and used the other output for 9V?
  19. berkeman

    Staff: Mentor

    Sure, whatever. Real world verusus the lab.
  20. Alright, cool. Thx for all the help. I will be sure to post results and pics once I finish it here within a month. That is, if I don't have anymore questions during that time :rofl:
  21. Well I'm back again. Since I have to order parts online, I have to wait a few days to work on the reciever/transmitter circuits. I figure I might as well make the stepper motor circuit while I have this free time. Could anyone supply me with a circuit in which I could do this?

    The stepper motor is supposed to sweep 180 deg, back and forth. The first my professor gave me was the L298 Dual Full-Bridge Driver.

    The other is the L297 Stepper Motor Controller.

    Edit: Here is the data sheet for the stepper motor
    Last edited: Nov 7, 2005
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