REMOTE SENSOR and CONTROL

Rev. B

J. Dunmire
August 12, 2003

Reference Documents:

Requirements
Schematic
Layout: Actual Size , Top , Bottom , Traces Only .
Signal List
Parts List

Introduction

MEEPS has four (4) sections:

CPU
Display
Sensor and Control Board
Remote Sensor and Control (Described here)

Detailed descriptions of each section can be view by clicking on the associated link above.

The Remote Sensor and Control section is one of the daughter boards of the Modular Embedded Experimenter's PIC System (MEEPS).

The remainder of this document describes the subsections of the Remote Sensor and Control daughter board, configuration options, and variations from the requirements.

Circuit Description

The Remote Sensor and Control Section (REMOTE) of MEEPS includes a prototying area that can be connected to the expansion connector on the MEEPS CPU, but it is primarily a standalone integration of the MEEPS CPU and SENSOR modules. The REMOTE module operates from a single AA battery and through the extensive use of surface mount components it fits in less than 2 cubic inches- including the battery.

Connectors

J401 - 1-Wire Bus
This connector allows connection to 1-Wire devices located off board. The pin out is the same as the connectors on the Display and Sensor modules.
1. Vcc
2. 1-Wire bus
3. GND
J402 and J403 - Antenna
These connectors are for antennas associated with U402 and U405. Both connectors have the same pin out. The connectors are used only when the associated RF devices (U40s and U405) are installed.
1. Antenna
2. GND
J404 - ICD2 Programmer
J404 is a 6 pin modular connector that mates with the cable from the MPLAB ICD2 Programmer/Debugger. The signals on this connector are connected to U408 and 409. They are also available at vias located in the prototying section of the board. The vias provide a way to connect the processors in the prototype area to the ICD2.
1. MCLR
2. Vcc
3. GND
4. PGD
5. PGC
6. Unused
J405 - High current digital outputs or spare I/O
J405 provides connections to the drain of the two (2) N-Channel MOSFET transistors driven by U409. These transistors are installed only if U409 is installed.
When U408 is installed the pins on this connector provide access to two of the unused signals from U408. The signals can be either inputs or outputs.
1. Q403b Drain (OUT_E) / U408_9 (RB0)
2. GND
3. Q403b Drain (OUT_F) / U408_12 (RB4)
4. GND
J406 - High current digital outputs
There are four (4) high current digital outputs available through J406. Each output is the drain connection from a N-Channel MOSFET transistor. These transistors are installed only if U408 is installed.
1. Q401b Drain (OUT_A)
2. GND
3. Q401a Drain (OUT_B)
4. GND
5. Q402a Drain (OUT_C)
6. GND
7. Q402b Drain (OUT_D)
8. GND

PCB Overview

The REMOTE PCB has the standard size and 40 pin connector required for a MEEPS daughterboard. The board can be sub-divided into two sections by cutting either between the prototyping section and U402/U405 or by cuttting along the edge of the battery.

Components are mounted on both sides of the PCB and parts on the underside of the board are covered by the battery holder.

The prototyping section includes two surface mount locations for 8-pin parts such as the PIC12F675. At the top edge of the prototyping section (when the 40 pin connector is located on the left) are vias connected to the power (Vcc) plane. A similar set of vias at the bottom edge are connected to the ground (GND) plane.

The prototyping area is not visible on the schematic because there are no signal connections.

The Vcc and GND pins on the 40 pin connector are not connected to the GND and Vcc planes of the REMOTE PCB. This prevents accident connections between the 3.3v power supply on the REMOTE module an the CPU power supply. If you want to use the 3.3v REMOTE module power supply to power the CPU, then make the appropriate connections between the 40 pin connector and the Vcc and GND vias at the top and bottom edges of the REMOTE module.

3.3v Power Supply

A step up DC-DC converter, U410, is the basis for the 3.3v power supply. It is designed to operate from a single battery. Note that there are alternate versions of U410 that can supply 5v. The higher voltage would be required if U405 is used.

Microcontrollers

The REMOTE module can be loaded with either a PIC18F1320 (U408) or a PIC12F675 (U409). Since U409 has very few I/O pins, not all of the feature of the REMOTE board can be installed at the same time when using U409.

Both processors use their internal clocks to reduce the component count. No external crystals or ceramic resonators are needed.

The microcontrollers are programmed, in-circuit, using MCLR, PGC and PCD pins available at J404. Connector J404 is a 6 pin modular connector suitable for connection to the MPLAB ICD2 debugger/programmer.

There is a blocking diode, D401, between MCLR and the Vcc supply so that high voltages (13v) on MCLR during programming will not damage other circuit components.

S401 allows signals GP0 and GP1 to be used as either I/O signals or programming pins. Depending on which sensor (U401 or U404) is loaded, the switch position for programming will be different. To program the procesor S401 should be place in the position that disconnects the sensor. S401 allows signals GP0 and GP1 to be used as either I/O signals or programming pins.

S401 is not needed when the U408 is installed.

Sensors

Up to three (3) sensors can be installed on the REMOTE module. U404, a SHT71, measures temperature and humidity. U401, an ADXL202E, measures acceleration (to 2G), and U407 can be a temperature sensor, a time module or a memory device. These devices are the same as the sensors on the SENSOR module.

The SHT71, U404, is a relative humidity and temperature sensor with a synchronous serial interface. The serial interface on the SHT71 is not an SPI or I2C interface. The clock signal, SCK, is connected to RA7, pin 18, on U408 and through switch S101 to GP1, pin 6, on U409. The data signal, DATA, is connected to RA7, pin 17, on U408 and through switch S101 to GP0, pin 7, on U409. The DATA signal is bi-directional, so RA6 (or GP0) will have to be switched from input to output as necessary to implement the STH71 communications protocol. Resistor R404 pulls the open drain signal from the SHT71 high when pin RA6 (or GP0)is configured as an input.

U407 is a 3-pin TO-92 1-Wire device such as the DS1822 or DS1821 temperature sensors. Some devices, such as the DS1822 but not the DS1821, can be used in a multi-drop 1-Wire bus. Connector J401 provides for off board expansion of the 1-Wire bus. The pinout for J401 is identical to the pinout for J202 on the Display and Basic I/O board.

1-Wire devices (U407 and any other devices connected to J401) are connected to signal RA4 on U408 and GP5 on U409.

ADXL202E, U401, is a dual-axis accelerometer. This device will measure accelerations up to 2G. The acceleration measurements are reported by pulse width modulation (PWM). The PWM signals are connected to RA1 and RA2 on U408 and, through switch S101, to GP0 and GP1 on U409.

The PWM period and the measurement bandwidth for U401 are set by R403, C402 and C403. With the values listed on the schematic (1.25 mega-ohms, and 0.47uf) the period and bandwidth are set for 10Hz operation.

Power for U401 is provided by setting signal RA0, of U408, high. This provides programmable control of the power to the ADXL202E. The data sheet for the ADXL202E provides details on how it can be operated in a power cycled mode to reduce the average power requirements.

If U408 is not installed, a jumper will need to be added to connect the power pin (pin 8) of U401 to Vcc.

High Digital Outputs

Four (4) high current, open drain, digital outputs are provided on connector J406 and two more on J405. The outputs are driven by N-channel MOSFET transistors; Q401-Q403. There are two transistors in each surface mount package. Each output is rated for 30 volts, output to ground, and 3.7 amps (limited by power dissipation).

RF Communications

There are two RF receivers and two RF transmitters that can be installed on the REMOTE module. They are not independent and only one receiver and one transmitter should be installed at one time. U403 and U406 are a TX and RX pair from the same manufacturer. Likewise U402 and U405 are a pair from another manufacturer. Both pairs operate on the same frequency, 433MHz. The U403/U406 pair have a higher bandwidth but are more expensive than the U402/U405 pair.

U405 is limited to 5v operation, so it should probably only be used when the REMOTE board is used as a daughterboard for the MEEPS CPU.

U403 and U406 have antenna connections on the radio module. Antenna connections for U402 and U405 are provided on the REMOTE module (J402 and J403 respectively).

The power supplies for U308 and U304 are filtered by R405 and C404.

The RX and TX data signals are connected to the UART built into U408 (RB3 and RB4). This provides a simple asynchronous data path for testing, but is probably not robust enough for reliable RF communications. Other signaling conventions can be implemented in software with the RB3 and RB4 pins configured for general I/O.

U409 drives the TX data using GP2 and receives RF data on GP4.

Variation from Requirements

The IrDA components were omitted from this module for two reasons. The first is space. The second reason is that IrDA communications requires rather precise baud settings and clocks that are not available when the processors are run using their internal clocks.

The Requirements did not specify a prototyping section on this board, but since one did not fit on the SENSOR module and there was spare space on this board, it was fairly simple to add the prototyping area.

$Date: 2008-10-21 19:17:34 $
$Revision: 1.5 $
$Source: /home/cvsroot/MEEPSTop/hardware/remote.html,v $ Contact me by email: jedunmire at gmail.com