need for angle sensor

[pravinchanm]

I am in need of angle sensor in order to measure the angle at the axis of robotic arm.. Else is their any other sensors which can do the angle measurement.. It should be comparatively cheaper.. I already tried it with potentiometer but each time there is a small variation in the range of milli volts which affects ma job

 

[hemanteda]

Not sure what you are willing to spend but you can explore ACCELEROMETER sensors (MEMS sensors) from Analog Devices or ST Micro. You can take a look at the link for element14 india site

Accelerometers | element14 India

They all connect to SPI bus

 

[chuckey]

You have not said what you are aiming to achieve -accuracy of .001 degrees or what? One thing you might have not thought about is the input impedance of the following stage as one source of error is the variable contact resistance of the "slider" which can cause additional voltage drops into the input of the amplifier and is easily rectified. To move from a high quality pot to a higher level of accuracy will be a hundredfold increase in complexity. Just as an after thought, have you seen those digital angle measuring meters*, about £50 over here, perhaps you can use one of those, suitablely modified.
* **broken link removed**
Frank

 

[pravinchanm]

@hemanteda : thank you for your reply..

But actually i need to measure the angle with reference to the prefixed reference. i don need to measure the angle moved or angular displacement or any of the case.. As how potentiometer always gives the constant voltage in its fixed position I need a sensor which always displays the angle with reference to the position it stays... Consider if i am switching off and on the power supply and angle should be displayed instantly in which angle it is..

---------- Post added at 17:19 ---------- Previous post was at 17:16 ----------

Accuracy of some 0.5 degree is more than enough !!

---------- Post added at 17:20 ---------- Previous post was at 17:19 ----------

Accuracy of some 0.5 degree is more than enough !!

 

[jpanhalt]

I have been playing with this Sears level: Sears: Online department store featuring appliances, tools, fitness equipment and more

It contains a MEMSIC (**broken link removed**) MXD2020E/F accelerometer module separate from the data module. On sale it is about $25 USD. The two modules communicate by simple serial. You may find hacking it easier than starting from scratch.

Also, if you search for "inclinometers" you may have more success than searching for "levels" or "angle finders."

John

 

[kak111]

Small magnetic encoders .................................

Magnetic Rotary Encoder IC austriamicrosystems

austriamicrosystems offers a range of Integrated Magnetic Rotary Encoders, from 8-bit incremental up to 12-bit absolut outputs. Or in other words, from 256 up to 16384 steps per revolution with serial, analog and PWM outputs for absolute position and quadrature. A simultaneous commutation output for Brushless DC (BLDC) motors is also available. These Magnetic Rotary Encoders are an ideal solution for replacement of both absolute and incremental optical encoders, potentiometers or rotary switches in a variety of industrial, consumer or even automotvie applications requiring precise angle sensing.

For ex.

12-bit Small Size Magnetic Rotary Encoder with Automatic Power Down and Wake-up Modes $ 3.35 /pc [ 1000pc`s ]

More info .......................
Rotary Encoders / Magnetic Encoders / Products / Home - austriamicrosystems AG

Regards KAK

 

[BradtheRad]

Perhaps by reading intensity of light through a semi-transparent strip?

The strip is light at one end and dark at the other. Gradual transition of grays in between. The grays can consist of black dots in varying concentrations. Or draw a long geometric shape narrow at one end and wide at the other.

Anchor one end to an arm of the robot.

Put a light detector and light emitter pair on the other arm.

The free end of the strip can slide back and forth between the detector and emitter.

The emitter shines onto one side of the strip. The detector reads intensity of light at the other side.

You'll need to calibrate arm distance versus voltage from the detector.

The elbow angle can be calculated by geometry.

 

[luben111]

Angle could be measured easily by using capacitive sensors on reasonable price. You can take some capacitive rotary slider and get directly the position.

 

[hemanteda]

@luben111 thats very interesting... I'm a little curious now, could you give some part numbers or links, I'll use them in one of my projects

 

[luben111]

There are many capacitive sensors on the market. I personally work with Atmel ones. Depend on the target resolution/precison there are many different possible solutions. For example for low resolution angle sensor I wold suggest to use one PCB with the pattern shown on the attachement, each electrode of the PCB is connected to one sensing pin of the capacitive sensor. In case you use Atmel you simply pick some standard uP and then you include in your project QTouch library (Free of charge from Atmel). At the end you have capacitive sensor plus some space to put your code in the same uP.

Mechanically you need to put some weight (disk) with diameter about 10-15mm connected to GND which stays close to the wheel elctrodes and distance <1mm and which is rotating (the center of the wheel and the center of weight rotation are identical). You can also use liquid as sensing object but you need to make seal it.

If you don't understand it and if I have some free time I could make some 3D model to show you how exactly the sensor is made mechanically.

The advantages of such approach is that you formally don't add additional components - you use the power of the existing uP to do capacitive sensing. What you need to add is a PCB with the elcectrodes (50mm diameter) and the weight which is rotating close to the electrode surface (electrode PCB is not moving, only the weight is rotating).

If you need some part numbers - ATXMega32 is extremely powerful, if you need cheap solution - ATTiny88 is the choise. Well, don't forget to add QTouch library to the project to turn the uP into capacitive sensor.

 

[hemanteda]

This is quite similar to microchip mTouch, I haven't tried it but I did see a demo at a Masters conference. It would be great if there is pre-built hardware module (like a potentiometer) which can be used directly

 

[JaCkIeSteVE]

An optional "tic" feature is available on the monitor. If the Sensor Pad senses movement, a tic sound will be heard into the Parents Units. The 'tic' sound can be disabled without removing the movement monitoring. This monitor detects baby's slightest movements and alerts you if absolutely no movement is detected for 20 seconds.

**broken link removed**