Sensor favorites

Think you'd be best off starting in hobby store catalogues, and see whats commonly available at reasonable prices:

In short, mechanical bumpers/switches , infrared range/obstacle detection, ultrasonic range finding , magnetic field sensors ( or compasses ). For odometry, people use various home-brew tachometers and encoders, some have successfully used motion detecing CCD sensors from optical mice. Cheap, easy-to-use accelerometers and gyros are just becoming available. Some relatively cheap camera systems are also available.

-kert

Hi,

One easy way to detect obstructions is to measure the motor current draw. This circuit was used in a small toy car that I retrofit the electronics. The LM324 at the bottom looks for a voltage proportional to motor current.

Nice and simple!

Do you have a suggestion for the wattage for the 1 ohm resistor? What have you found to be adeuate for these toy cars? I looked on the toycar.html page and didn't see it mentioned.

Your Web page is quite impressive, BTW.

-- Gordon Author: Constructing Robot Bases (Forthcoming) Robot Builder's Sourcebook, Robot Builder's Bonanza

I missed the initial part of the thread, so I'll reply through this one, and also echo the usefulness of checking out Acroname and others.

Besides simple mechanical switches for touch, the most common specific electronic sensors I see on robots are:

1. Sharp GP2xxxx series distance judgement/measurement. Different models available, including analog and serial digital. More and more MCUs have onboard ADCs, and I'm seeing a preference for the digital output sensors.
2. Devantech SRF04 (and SRF08) ultrasonic modules. These are quite popular, possibly among the most widely used sensor type for hobby robots following the Sharps.
3. Various implementations of IRPD, using a Sharp or Panasonic or LiteOn or similar infrared demodulator, and modulated LEDs. Can use a co-processor MCU or TTL steering logic; lots of variations but the outputs tend to be simple two bit, one bit each for left and right proximity. Needs little to interface to MCU
4. Fairchild QRB1134 IR retroreflector (and similar units). These are single unit IR emitted and detector, most commonly used for line following, edge detection for sumo, and similar tasks. When used with a comparator the output is one bit on/off. Needs little to interface to MCU.
5. CdS photocell. The chief benefit is its analog output, so these need an ADC input.

Less commonly used, but still popular on tons of robots:

A. Devantech CMPS03 digital compass. B. Analog Devices ADXL202E accelerometer, and lower-cost versions from Memsic. C. UVTron flame sensor (mostly for fire fighting robots). D. PIR sensors, either the Eltec (a bit expensive, but very easy to use) or hacked security modules. Output is 1-bit digial.

Gaining in popularity are rate gyros and some solid-state gryos, like those from Analog. These are used to build self-balancing robots, a la Segway.

-- Gordon Author: Constructing Robot Bases (Forthcoming) Robot Builder's Sourcebook, Robot Builder's Bonanza

I meant analog output.

-- Gordon Author: Constructing Robot Bases (Forthcoming) Robot Builder's Sourcebook, Robot Builder's Bonanza

Interesting approach for a bump detector. I will defineately support both the A-D and 324 versions. It will also be employed as a drag sensor to tell when the robot is pushing or pulling something.

--Ryan

It was a 1/2 watt but that is probably overkill....

Max of 1/2 amp at 1 ohm: P= I*I*R = 1/4 watt worst case.

My later designs used an a/d and 0.1 ohms (for currents under 1 amp). Then I checked for motor stall condition in sofrware. This way I could ignore the 'start up' current and also measure 'normal' current to tell when I actually hit an object.

My electronics skills is not much beyond LED circuits and building circuits from existing schematics. What is the schematic for measuring motor current for 12v motors that draw a max of 5 amps stalled (about 1.4 amps with no load)? My MCU has 0-5 volt ADC inputs. Thanks for any help!!!

-C