Subject:
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Analogue sonar design.
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Newsgroups:
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lugnet.robotics.handyboard
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Date:
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Tue, 25 Aug 1998 20:08:07 GMT
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Original-From:
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Jeroen van der Vegt <a.j.vandervegt@#NoSpam#its.tudelft.nl>
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Viewed:
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1231 times
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Hi all,
I'm trying to build a sonar circuit and connect it to my HandyBoard. I know
Polaroid makes one, but I have no idea where to get it for little in Europe.
I try to keep the interface as simple as possible, and I'll probably be
using three signal wires:
1. A signal from the HB to the sonar-circuit, which should activate it -
I want to set a flip-flop with it, and make sure it doesn't really matter
how long the 'enable' signal is.
2. A digital signal from the circuit to the HB to send a signal when the
measurement has been completed.
3. An analogue signal from the circuit to the HB, which will represent
the distance measured by the sonar.
Apart from these, there of course are 0V, 5V and perhaps 10V (directly from
the battery, for the OpAmps). I'm also not sure yet wheter I'll be using the
HB clock, or if I'm going to create a clock on the sonar board. The latter
can quite easily be done using a 4060 chip - a 14 bit counter with internal
oscillator, which I can use to count the number of pulses send at the same
time.
I've found the page on sonar at www.wizard.org, which gives an exellent
explanation and circuit, and I'll be using the analogue circuits (the
amplifier circuit, and the little circuit connected to the transmitting
ultrasonic transducer) found there. I don't want to use the complete timing
circuitry, since it would take at least four of the HB's digital inputs. I
know I could use a D/A converter, which would probably be the easiest
solution. But I would like to use as little IC's as possible, and it would
be quite strange to convert a analogue signal (the time sounds needs to
travel is analogue) to digital, than to an analogue signal (in the D/A
converter), and back to digital in the HB.
I want to create the analogue signal by (dis)charging a capacitor when the
sonar starts beeping, and I want to read the voltage over the capacitor when
a return signal is detected. The problem is, I don't know whether I can read
a capacitor before it has (dis)charged completely, since the 6811 has to
wait for a 'signal valid' signal on a digital input, and then it has to read
an analogue input (which might take too long, especially if more programs
are running). Also the input capacitance (and 48K resistance!) of the HB
inputs could perhaps influence my readings.
Does anybody have any idea whether using a analogue input is a good idea,
and which size the capacitor should have at least for use with such an
input. A circuit which can store a analogue value would be ideal, but I
don't think something like that exists.
(Original) idea's are also appreciated!
Thanks in advance,
Jeroen van der Vegt.
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