Adcon Telemetry A720 Revised technical manual with schematics and parts lists removed
A720 – addIT™
Technical Documentation
Adcon Telemetry GmbH
Inkustr. 24, A-3400 Klosterneuburg
Austria
Tel: +43-2243-38280
Fax: +43-2243-38280-6
http://www.adcon.at
Adcon Telemetry, Inc.
1001 Yamato Road, Suite #305, Boca Raton, FL 33431
USA
Tel: +1-561-989-5309
Fax: +1-561-989-5310
http://www.adcon.com
Adcon Telemetry srl.
Bd. Ana Ipãtescu nr. 27 ap. 11 R-71111 Bucharest
Romania
Tel: +40-1-312-6886
Fax: +40-1-312-6668
http://www.adcon.ro
Proprietary Notice:
The Adcon logo, the A730 series, addIT™, addVANTAGE and
AgroExpert™ are trademarks or registered trademarks of Adcon Telemetry
GmbH. All other registered names used throughout this publication are
trademarks of their respective owners.
This publication contains confidential information property of Adcon
Telemetry GmbH. Disclosure to third parties of the information contained
herein is prohibited. Neither the whole nor any part of the information
contained in this publication may be reproduced in any material form
except with the prior written permission of Adcon Telemetry GmbH.
Release 1.0, October 1998
Copyright ©1998 by Adcon Telemetry GmbH.
All rights reserved.
Table of Contents
1. About the A720 5
2. Hardware 6
2.1. The Radio Unit 6
2.1.1. Receiver Section 6
2.1.2. Synthesizer Section 8
2.1.3. Transmitter Section 9
2.2. The Modem Interface 9
2.3. The Microcontroller and the Power Management Sections 10
2.4. The Interface Board 11
3. Tuning Procedure 12
3.1. Programming the Boards 13
3.2. Setting-up the Default Parameters 13
3.3. Tuning 13
3.3.1. Definitions 14
3.3.2. Test Equipment Settings 15
3.3.2.1. Network Analyzer (HP 8711) 15
3.3.2.2. Service Monitor (Rohde & Schwarz CMS50) 15
3.3.3. Adjusting the Receiver Front End 16
3.3.4. Adjusting the VCOs 17
3.3.5. Checking the Receiver Parameters 17
3.3.6. Checking the Transmitter Parameters 18
3.3.7. Data Transfer Check 18
3.4. Additional Issues Related to Type Approval Testing 19
3
3.4.1. Controlling the Unit 19
3.4.2. External Power Supply 19
3.4.3. Specifications 20
3.4.4. Bill of Materials 24
3.4.5. Device Photographs 29
4. Software 34
4.1. AMOS 34
4.1.1. Initialization 35
4.1.2. 1/2 Second Interrupt 36
4.1.3. Pulse Counters Interrupt 36
4.2. Mode Check 36
4.3. A/D Task 38
4.4. The Terminal Task 39
4.4.1. Supported Commands 39
4.4.1.1. The SET Series of Commands 39
4.4.1.2. Querying the Actual Configuration Parameters 41
4.5. The Radio Interface Task 41
4.5.1. Digital Squelch 42
4.5.2. Modulation Technique Used 43
4.5.3. Generic Format of a Radio Frame 44
4.5.4. Data Frames 45
4.5.5. Frame Types 45
4.5.5.1. Request 45
4.5.5.2. Broadcast Answer 46
4.5.5.3. Set I/O Request 46
4.5.5.4. Read I/O Answer 47
4.5.5.5. Broadcast Request 47
4.5.5.6. Ping 47
4.5.5.7. Pong 47
4.5.5.8. Memory Dump Request 48
4.5.5.9. Memory Dump Answer 49
4.5.5.10. Data 49
4.5.5.11. Set ID 50
4.5.5.12. Set Slot Time and Sample Rate 50
4.5.5.13. Set Frequency 50
4.5.5.14. Set Battery Charge Levels 51
4.5.5.15. Set Pulse Counters Parameters 51
4.5.5.16. General Acknowledge 51
4
Wireless Sensor Interface A720 (addIT™)
1. About the A720
The A720 Wireless Sensor Interface (also known as
range telemetry device, capable of sampling up to 6 analog sensors and 4 digital inputs (of which 2 counter types); in addition, it can control two relays.
The frequency of operation is in the 432 to 470 MHz range, making it adaptable to
most radio communication regulations in the world. The output power is under 10
mW, while the modulation is narrow band FM (12.5 or 25 kHz channel spacing).
Due to its construction, as well as to the software controlling it, the power consumption is extremely low (average 6 mW). The unit operates from a built in NiCd 6.2 Volt
rechargeable battery, which is charged either using an 600mW solar panel or an external power supply adapter. A special configuration may be implemented where no
internal battery is used, rather the power is obtained exclusively over an external
connector.
The A720 is a ruggedized unit, complying with the IP65 environmental protection
class (NEMA 4). It can be easily installed and it integrates perfectly in an Adcon A730
system. Depending on the terrain, it assures a reliable wireless connection to an
A730MD or A730SD device to distances up to 800 meters, under favorable conditions
even more.
addIT™
) is a low power, short
5
Wireless Sensor Interface A720 (addIT™)
2. Hardware
Most of the electronics are situated on the main board, while an interface board is
used to connect the unit to the outside world. The main board contains a radio unit,
a low speed modem interface, a microcontroller and a power management subsystem.
Antenna
Radio Unit
Modem
Interface
External Power
System Supply
Battery
For further details you may want to consult the schematic diagram located on page 7.
2.1. The Radio Unit
It consists of a RF transceiver, that conforms or surpasses the ETSI 300 220 specifications. The receiver is a double superheterodyne type, first oscillator being synthesized. The transmitter is also synthesized, only the PLL chip and the frequency
reference being common (there are two separate VCOs, one for the receiver’s local
oscillator and another for the transmitter).
2.1.1. Receiver Section
The antenna signal is fed through a low pass filter and the antenna switch (D1/D2)
to a helical band-pass filter (it has a 20 MHz passband at 3dB), which attenuates the
first image and the oscillator fed-through signal. A cascode chip (U3) is used for RF
signal preamplification and first mixer, the LO being fed via the second emitter of the
cascode. The resulting IF on 45 MHz is filtered through XF1 which in this case provides the image attenuation for the second mixer.
Digital I/O
µController
ADC
4
6
Analog Inputs
Power
Management
After a pre-amplification by means of the transistor Q11, the 45 MHz IF signal is applied to U10, which provides the second frequency change to 455 kHz, pre-amplification, limiting and FM demodulation. The second oscillator is also built into this
6
Wireless Sensor Interface A720 (addIT™)
chip, a third-overtone quartz oscillator oscillating on 44.545 MHz. The 12.5/25 kHz
selectivity is obtained through the use of the two ceramic filters CF1 and CF2 (version GX for 12.5 kHz or EX for 25 kHz channel spacing), exhibiting a low group delay
time. An interesting feature of U10 is its coilless demodulator, which is PLL based.
By adjusting R67 and R60 one can change the bandwidth and the central frequency
of the IF demodulator.
The data signal is obtained on pin 17 of U10 and is buffered by means of U8:D. In
addition to the data signal, an RSSI signal is obtained on the pin 18 of the same U10.
The signal is multiplexed with other DC signals (battery level and on-board temperature) by means of U6 and U7 and then is presented to one of the A/D inputs of the
microcontroller.
The entire receiver section is enabled by the microcontroller through Q8.
2.1.2. Synthesizer Section
The synthesizer is based on a very low power PLL chip, U2. An important feature of
the chip is its FastLock™ mechanism, which improves the locking speed of the loop
without compromising on the VCO noise. The operation of the PLL chip is directed
by the microcontroller (operating frequency and channel step) and are therefore fully
under software control. The frequency reference is obtained from the highly stable
temperature compensated crystal oscillator OSC1.
There are two separated VCOs: one for the receiver section and a second for the
transmitter section. The receiver oscillator is 45 MHz higher than the transmitter oscillator, the latter being on the programmed operating frequency. This solution optimizes the operating range of the individual VCOs, and keeps the noise level down.
The receiver VCO is realized with Q6 as oscillator and Q4 as buffer/amplifier, while
the transmitter VCO with the pair Q2/Q1. The configuration of the two VCOs is very
similar: in order to minimize the power consumption, the transistors are connected
in series from a DC perspective, the buffer being the load of the oscillator.
A small amount of RF from each VCO is fed to the PLL chip input (to the internal
prescaler) by means of the group C47/R27, and C16/R7 respectively. The output of
the PLL from the phase comparator/charge pump is filtered by means of the low
pass filter formed by C35/R29/C36/R22/C55 and applied to the two varicap diodes
D4 and D3. In addition, the FastLock mechanism occasionally activates R21 to increase the current of the charge pump (you may want to consult National Semiconductor’s Application Note AN-1000 “A Fast Locking Scheme for PLL Frequency
Synthesizers”, by D. Byrd, C. Davis, W.O. Keese, July 1995 for additional details on
the FastLock mechanism).
8
2.1.3. Transmitter Section
The transmitter section uses the VCO composed by Q2/Q1. This VCO is modulated
on the anode of its varicap diode (D3) by means of a small amount of the data signal.
Before modulation, the data signal is filtered by a four-pole low-pass filter built
around U1. The filter effectively removes the harmonics on the data signal in order
to keep the adjacent channel power under the required level.
The output of the VCO/buffer amplifier is applied to the power amplifier, operating
in class A thus minimizing the harmonics (Q3). The output of the amplifier is directed to the antenna through the antenna switch and the low pas filter. The antenna is
switched on transmit mode when a positive current is applied on the anode of D1 via
R12. The DC component is obtained from the collector of the power amplifier (Q3).
C11 is used to pass along the RF component.
The transmitter is activated by the microcontroller in two steps:
• The PLL is switched on (by means of Q5);
• After a delay of about 5 mS when the PLL has settled, the power amplifier is
switched on (by means of Q7).
The above mechanism assures a clean transmission start, avoiding that the transmitter “spills-out” its carrier on several channels before stabilizing. The switch off follows the same principles, but in a reverse order.
The Modem Interface
2.2. The Modem Interface
The modem operates with two tones: 1 kHz (representing the 1 bits) and 2 kHz (representing the 0 bits). A bit cell is represented by a complete time period (
raw throughput varies between 1 and 2 kbps (average 1.5 kbps). The modem functionality is essentially implemented in software. However, a signal conditioning is
performed on both receive and transmit paths.
On receive, the buffered analog data signal from U8:D is applied to a 3 kHz low pass
filter (U8:A). The filter output is further fed both to a Schmidt trigger (U8:C) and a 50
Hz low pass filter (U8:B), the output of the latter being used as a reference for the slicer (the Schmidt trigger). The TTL data,
(i.e. on TP2). The microcontroller overtakes the decoding operation (see also “Modulation Technique Used” on page 43).
On transmit, only the low pass filter built around U1 is used: its role is to “smooth”
the square signal
TXDI
generated by the microcontroller.
RXDO
, is obtained at the output of the slicer
1/f
), thus the
9
Wireless Sensor Interface A720 (addIT™)
2.3. The Microcontroller and the Power Management Sections
The operation of the whole unit is under the control of U9, a PIC16C77L microcontroller. It is a powerful chip exhibiting an extreme low power consumption. Its main
jobs are:
• Controls the radio unit;
• Implements the modem functionality;
• Assembles the radio frames and waits for requests from a remote;
• Performs the sampling of the sensor inputs and the A/D conversion;
• Stores the values in a local FIFO; manages the FIFO;
• Implements the pulse counter function;
• Increments the Real-time clock;
• Assures the power management;
• Implements a serial Command Line Interface (CLI).
Note: For more details on some of these functions, see also the chapter “Software” on page 34.
The chip operates at its maximum speed, in this case 4 MHz (the “L” version) and
uses a crystal (X1). The real time clock is implemented by means of a 32.768 kHz crystal (X3) connected on the internal TIMER1.
The radio unit is controlled via the SPI bus on one hand (to set the PLL chip parameters) and via the switches Q8 (for receive) and Q5/Q7 (transmit). As already mentioned, the modem is implemented in software: the output signal is available on RB1
TXDI
(
), while the receiver output is fed on the RB0/INT pin (
The A/D subsystem is used to sample the inputs (AN0 to AN5); the 7th analog input
is used for on-board measurements (local battery, internal temperature and RSSI signal, switched by means of the analog switches U6 and U7); a stable 2.5 Volt reference
supplied by U4 is applied to the RA3/AN3/Vref pin. The reference is powered by
the microcontroller only when sampling the A/D inputs. The external sensors are
powered through U13.
The sampled input values are stored in a FIFO built with a serial EEPROM chip, U5.
These values may be retrieved when a pertinent request is received over radio, or
over the serial line. Additional configuration parameters are stored in the EEPROM,
e.g. the serial number of the device, the operating frequency, etc.
The pulse counter functionality is implemented by means of the two inputs RB6 and
RB7, based on the
microcontrollers.
The power management controls the charge/discharge of the battery (via Q9 and
U11), senses the misery levels and switches off the unit in order to protect the battery
(again U11). In addition, the software senses a storage condition, where no activities
interrupt on change
feature implemented in the PIC16C7x series of
RXDO
).
10
must be performed thus driving the unit in the hibernation mode. If the unit was
completely switched off due to an extremely low battery level, Q10 would start it up
again only if external power is applied to the power connector (e.g. from a solar panel).
The terminal mode is implemented by means of the built-in UART. No on-board level drivers are present in order to minimize power consumption; a special adapter cable that performs the TTL to RS232 level shift and vice-versa is available. By means
of this cable and using the implemented commands, various parameters can be
changed/configured (see also the chapter “Software” on page 34).
2.4. The Interface Board
The interface board assures the connection between the main board described above
and the outside world. It contains the three connectors (
some passive components protecting the pulse inputs. Each of the
accept:
• Three analog inputs;
• One digital Input or Output (its functionality can be switched remotely);
The Interface Board
I/O A, I/O B
and
POWER
connectors can
I/O
) and
• One pulse counter input.
POWER
The
connectors allows for:
• External supply (battery or any DC source from 5 to 10 volts);
• External charge supply (either a solar panel or an AC adaptor) if an internal
rechargeable battery is used;
• Communication over serial lines, at 19200 baud.
Note: The serial line is TTL compatible, a special adaptor cable must be used to reach the RS-232
levels. If an external battery is used, then the internal battery must be disconnected.
11
3.1. Programming the Boards
This section will be completed later.
3.2. Setting-up the Default Parameters
The tuning procedure is not possible without first configuring some default parameters on each unit. This is done using a special serial cable connected between the
A720MB with an A720CA interface to a PC; in addition, a communication terminal
program (e.g. Hyperterminal, in Microsoft® Windows™ 95) is needed to send the
commands. The terminal program must be configured as follows:
Programming the Boards
• 19200 Baud
• 1 Stop bit
• No parity
• No protocol (neither hardware, nor software)
To check that the communication is operational, press the
appear on the terminal screen. Using the
SET
command, following default parame-
Battery
Ext Power
ENTER
4
Ground
key: an OK should
5
3
RxD
1
2
TxD
ters must be pre-loaded (for more details on the meaning of the commands, consult
the section “The Terminal Task” on page 39):
SET OWNID 1
SET PMP 65 72
SET SLOT 900 3
SET RSSI 58
SET BL 432000000 450000000
SET FREQ 432000000 25000
The last two
SET
commands are valid for the units that will be trimmed for the low
band; for the high band, they must be replaced by:
SET BL 450000000 470000000
SET FREQ 450000000 25000
Note: The SET BL command sets the band limits, while SET FREQ sets the operating frequency;
before shipping and depending on the target country these two parameters may be changed.
The SET BL command must be issued always before the SET FREQ command.
3.3. Tuning
The tuning can be performed only after the units are programmed and the default
parameters are set, as described previously.
13
Wireless Sensor Interface A720 (addIT™)
3.3.1. Definitions
The diagram of the setup environment is depicted in
Scope Service Monitor Network Analyzer
Figure 3.
Voltmeter
0.765 V
Optional
Figure 2.
Testing
Fixture
Trimming Setup.
Out
Scope
In/Out
Service
Monitor
Power/
Sens
In
Network
Analyzer
Out
Voltmeter
Wobble
Out
Network
Analyzer
A720MB
Connector
RS232 To/From PC
+
6.5 V
–
The testing fixture is used to fasten the PCB under test both mechanically and electrically in such a way to allow its rapid and comfortable trimming. It consists of a mechanical breadboard with two screws that are used to fasten the board; 5 elastic pins
are used to transport the relevant signals from the PCB to their corresponding apparatus test cables. In addition, a switch (
Power/Sens. <–> Wobble
) allows switching of
the antenna input/output to the network analyzer or to the service monitor. The
schematic diagram of the testing fixture is depicted in
Figure 3.
14
Figure 3.
Scope
Service
Monitor
In Network
Analyzer
Out Network
Analyzer
12 KW
Power/Sens.
Wobble
680 W
Schematic Diagram of the Testing Fixture.
TP4
Gnd
Ant
TP2
TP1
A720MB
1 MW
Voltmeter
There are only three tuning elements to be acted upon: FL3, L6 and L10. Their location on the PCB (all upper side) is depicted in the schematic below:
3.3.2. Test Equipment Settings
Before proceeding, certain controls on the test equipment must be set; some of the
settings depend of the operating band (high or low) of the device under test (DUT).
In addition, it is highly recommended that the ambient temperature during trimming is 24° C (±2°C).
3.3.2.1. Network Analyzer (HP 8711)
Tuning
FL3
L10
L6
The settings for the Network Analyzer are as follows:
• Center frequency: 450 MHz
• Span: 100 MHz
• Display: 5.0 dB/div
• Power: -20 dBm
• Markers:
— low band Mkr1 – 440 MHz, Mkr2 – 430 MHz, Mkr3 – 450 MHz;
— high band Mkr1 – 460 MHz, Mkr2 – 450 MHz, Mkr3 – 470 MHz.
Note: A good idea is to store the instrument state for the two settings, low band and high band.
3.3.2.2. Service Monitor (Rohde & Schwarz CMS50)
The setting for the receiver section check are as follows (RX-TEST):
• SET RF: 432000000 Hz (Low band) / 450000000 Hz (High Band);
• RF LEV: 5 µV (see also note below);
• SINAD;
• AF1: 2kHz;
• MOD1: 3.5 kHz;
• SCOPE MODE;
• BEST RANGE.
15
Wireless Sensor Interface A720 (addIT™)
The settings for the transmitter section check (TX-TEST):
• COUNT: (should show the transmitter carrier frequency);
• POWER: (should show the transmitter carrier power).
Note: If using the Testing Fixture, a calibration should be performed to check the losses in the an-
tenna switch, cables, etc. Depending on these losses (which at 450 MHz can amount up to 6
dB), it may be needed to adjust the RF LEV value accordingly (up to 10 µV). Similarly, the
measured output power must be correspondingly downgraded (see also “Checking the Transmitter Parameters” on page 18).
3.3.3. Adjusting the Receiver Front End
• Mount the DUT on the testing fixture and connect it to the PC via the serial
cable;
• Select the appropriate instrument profile depending on the device’s band
(High or Low);
• Turn on the receive subsystem of the DUT by entering the RX command at the
terminal;
• Check that the switch on the Testing Fixture is in the
Wobble
position;
• Adjust the filter FL3 until you obtain a curve similar with one of those shown
in
Figure 4.
(depending on the band); this is done by successively adjusting the
two trimming screws located on the filter.
If this is not possible, check the power supply, the cable connections to/from the test
equipment, etc. In addition, verify if you have approx. 1.1 volts on the test point TP4.
Finally, check if all 8 pins of the filter FL3 are properly soldered.
Low Band High Band
16
Figure 4.
Helical filter’s diagrams for Low Band and High Band devices.
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