Serial Interface and Sensor Software
(Last Updated 12/2006)
(Last Updated 12/2006)
(zip, 267,834 bytes)
** Click on boxes in diagram for more information.
Check out our Flash Demo to see how capacitive sensing technology is changing the user interface experience.
Implementing a touch sensor solution using the AD714x requires three components: the AD714x capacitive-to-digital converter IC, sensors on a PCB or Flex Circuit, and software to communicate with the AD714x.
Our standard sensor library is available in a PADS Mentor Graphics™ format allowing the design of your own unique sensor interface layout. Before downloading the sensor library it's recommended you become familiar with the various sensor layout configurations. Read application note AN-854, "Sensor PCB Design Guidelines for the AD714x Capacitance-to-Digital Converters".
The standard software supports both I2C™ and SPI™ buttons and 8-way switches. Before downloading the software, it's recommended that you read application note, "Introduction to AD7142 Host Software Requirements", in the applications section. Comprehensive AD7142 and AD7143 datasheets, which are available to download, are complete with configuration and programming guidelines.
I2C Basic Configuration (zip, 55,419 bytes)
I2C 4 Buttons (zip, 58,934 bytes)
I2C 8 Way Switch (zip, 56,961 bytes)
The SPI software downloads apply to the AD7142 only.
SPI Basic Configuration (zip, 45,694 bytes)
SPI 4 Buttons (zip, 49,181 bytes)
SPI 8 Way Switch (zip, 49,258 bytes)
In addition to the button and 8-way switch software we also provide slider and scroll software. In order to obtain those additional software routines we require you to print and sign three copies of our software license agreement. Click here (pdf 31,544 bytes) for the PDF version of the document. Send the signed copies to the following address:
Analog Devices, B.V.
Raheen Business Park
Attention: Garry O’Neill
Can other components go on same PCB as sensor?
Yes, other components, for example LEDs, connectors, other I.C.s, can go on the same sensor PCB as the sensors. The only caveat with this: the sensor PCB must be glued or taped to the covering material to prevent air gaps, so the placement of any other components on the sensor must take this into account. It is recommended that the AD714x go on the back side of the sensor PCB.
Is an air gap between sensor PCB and covering material allowed?
No air gap is allowed between the sensor PCB and the covering material or case of the product. Less of the electric field extends above plastic when there is an air gap, and the field dissipates in air. These combine to decrease the sensor response. Also, the plastic or other covering material may bend on contact, and the user may interfere with more or less of the electric field than before. This results in a non linear response from the sensor. These two effects combine to give an unpredictable response from sensor, making it unusable.
3M 467MP double-sided tape or similar to - glue or tape the sensor PCB to covering plastic.
2-layer or 4-layer PCB?
Choose a 4-layer PCB design when there is no room to route from the AD714x to and from the sensors, outside of the sensor active areas. If there is room on the PCB to route to and from the AD714x, then a 2-layer PCB can be used.
What is the maximum distance between sensor traces and AD714x?
Maximum distance between sensor trace and AD714x CIN input pin is 10 cm. However, one sensor can be 10 cm from the AD714x in one direction, while another is 10 cm from the AD714x in the opposite direction, giving 20 cm between sensors.
Is there a keep out area required around the sensor?
Yes. For grounded metal, the keep out is 0.2 mm. For floating metal, keep-out area is 5 cm. Floating metal closer to the sensors than 5 cm should be grounded.
How many sensors can I implement using one AD714x device?
The number of sensors that can be implemented using one AD714x depends on the type of sensors required. The AD714x has 14 input pins, and has 12 time based conversion stages. The table below gives a the number of input pins and the number of conversion stages required for each sensor type. Any number of sensors can be combined, as long as the total number of inputs required does not exceed 14, and the total number of stages required doe not exceed 12.
|Sensor Type||# of Cin Inputs Required||# of Conversion Stages Required|
|Button||1||1 or 0.5 for differential operation|
|8-way Switch||4 – top, bottom, left & right||3|
|Slider||8 – one per segment||8 – one per segment|
|Wheel||8 – one per segment||8 – one per segment|
|Key pad||1 per row, 1 per column||1 per row, 1 per column|
Can all sensors connected to the AD714x be active at the same time?
The AD714x takes a measurement on all sensors connected to it in a round robin fashion. All sensors can be measured within 40 ms. In practice, this allows the AD714x to detect if sensors are active at the same time, as it is very unlikely the end user can activate/deactive a sensor within 40 ms.
What happens when a finger is placed across two sensor buttons?
If the two buttons are adjacent to each other and never meant to be activated at the same time, the AD714x CDC converter stages can be configured differentially to null out the effects of a user simultaneously touching two buttons. Alternatively, the AD714x can be configured to register both sensor contacts at the same time.
What happens when users with different finger sizes contact the sensor?
The AD714x internal logic contains an Adaptive Threshold algorithm that automatically adapts to the users finger size and readjusts the threshold levels accordingly.
Will the AD714x sensors work with a glove?
Some gloves will work while contacting the sensors but on the other hand, some gloves will not, depending on the thickness of the glove. ADI have tested gloves of 2 mm thickness and have found this to work successfully.
Can conductive material be placed directly on top of the sensors?
Yes, but the AD714x may detect this as a contact and assert the interrupt output.
Can the AD714x work under wet/humid conditions?
Like any capacitive sensor application, the sensors performance will be affected by water and humidity. The AD714x internal environmental algorithms will automatically track and correct for humidity conditions. Water conditions (especially saturated) become more challenging and need to be evaluated carefully for each application.
How far away from the sensor can proximity be detected?
This will depend on the size of the sensor. Applications can be easily developed where proximity can be detected up to a few millimetres from the surface of the sensor. The AD714x evaluation board can be used to experiment with proximity detection.
Is there a power-up configuration?
Yes, the AD714x BANK 2 connection set up registers and some BANK 1 set up registers have to be configured at start-up.
Is auto calibration possible?
Yes, the AD714x internal logic contains two calibration algorithms for correcting drift errors due to environmental (e.g., temperature and humidity) conditions.
What is the IC temperature range?
The AD714x is specified at -40°C to +85°C.
What is the AD714x operating voltage range?
VCC = 2.6V to 3.6V
VDRIVE = 1.65V to 3.6V
Does the AD714x have an interrupt?
Yes, the AD714x interrupt can be configured to be asserted at the end of each CDC conversion cycle or only upon user contact with a sensor.
Should I be concerned about ESD?
The AD714x ESD Human Body Model is specified at 2.5kV.
The AD714x sensors have been subjected to the ESD air discharge up to 15kV under both contact and non-contact conditions without any failures. Note: ESD events have to be carefully considered during development in order to prevent the ESD charge from coupling directly onto the AD714x sensor board circuits.
Does Analog Devices provide the open source C-Code for sliders and sc rollers?
Yes, the code is provided free of charge and royalties once the customer signs the AD714x SW licence agreement.
What is the code space for a Slider?
Typically: 500 Bytes of Data Memory and 8Kbytes of Code Memory.
What is the code space for a Scroll Wheel?
Typically: 600 Bytes of Data Memory and 10Kbytes of Code Memory.
Does Analog Devices provide an AD7142 evaluation board?
Yes, an evaluation board including the GUI SW can be purchased online at www.analog.com/AD7142.
Does Analog Devices provide an AD7143 evaluation board?
Yes, an evaluation board including the GUI SW can be purchased online at www.analog.com/AD7143.