- DrDAQ operation showing long term stability & Mains outages
SYSTEM SPECIFICATIONS
This RS485 COMM System developed for remoting sensors of PICOLOG Data Acquisition Loggers such as: DrDAQ, Picolog 1012 & 1016 and others.
Transmission standard.............................RS485
Transmission medium 1...........................Standard twisted pair + common ground conductor or
Transmission medium 2...........................Twin coaxial line with shields as common ground.
Nominal line impedance..........................60/120 Ohm. 60 Ohm used to minimise reflections.
Operating temperature range (*)..................0 to 40 °C.
System in/out voltage transmission range......0 to 2500 mV, negative common.
System Resolution (**).............................8 bit or 9.8 mV over the dynamic range.
System accuracy....................................+/- 5mV within stated temperature range.
System Sensor input impedance..................> 0.5 MOhm (Slave inputs).
System output impedance(***)..................1 MOhm (requires 1 MOHm load or better).
System Voltage reference.........................2500 mV.
Line transmission speed............................58600 Baud. Lower speeds possible by software.
PC (USB) transmission speed......................115200 Baud. Lower speeds possible by software.
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Software programmable settings(****)
Number of Iterations k...........................up to several million.
Minimum recycle time t..........................30 Millis (1000 Millis = 1sec. approx.).
Maximum recycle frequency.......................25 Hz approx.
Byte/Analogue conversion factor................cal. = 9.8 for V. Reference = 2.5 V.
restLvl – preset fixed Slave level................127 corresp. to 1250 m V with mains failure.
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Serial Monitor programmable settings
Line transmission speeds........................4800, 9600, 14400, 19200, 28800, 38400, 56600 Baud
USB transmission speeds.........................same as above, plus 115200 Baud.
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Master hardware support..........................Laptop PC with USB upload, control & Serial Mon.
Master supply voltage..............................USB bus, +5V Nom.
Master consumption from USB Bus................< 100 mA.
Slave hardware support............................Laptop PC for USB sketch upload & checking only.
Slave operating support............................Self standing with external +9V Linear PSU.
Slave consumption from +9V PSU.................<100 mA.
Linear PSU requirements...........................9V +/-2V, ripple & noise max: < 40 mV p.p.
Master & Slave software support..................Windows Xp & Windows 7 (tested).
Recommended Arduino 1 IDE.......................1.0.6 with ERW enhancement 1.05.
Recommended PC operating System...............Windows XP.
(*) Microprocessor is rated -45 to + 55°C. The Sytem has been tested in rated range of 0 to 40°C.
(**) Depends on Microprocessor used. More recent devices will allow up to 16 Bit Resolution.
(***) Depends on PWM filtering method. For RC filtering output impedance very high. If low output impedance required, use Operational Amplifier 3 pole Chebyshev Active filters as shown in previous postings.
(****) Software settings written in the sketch, as seldom changed. Serial Monitor parameter setting possible with sketch modification.
NEW SKETCH RELEASE
I have uploaded in the next REPLY: sketch_MASTER_485_7_7 and sketch_SLAVE_485_7_3 for operation with Slave working barefoot. Sketches are in WORD format as the previous ones.
a) Download each word file and copy and paste contents on a new blank IDE sketch.
b) Carefully check all entries of each sketch & compile it. Most problems are given by wrongly transferred inverted commas (“ “) or by missing interdict (// or /*, */) characters.
c) Connect Master & Slave units through the twisted wire line simulator.
d) Connect Slave to linear + 9V supply.
e) Connect Master & Slave to own laptops.
f) LEDS on Micros should turn on.
g) Check Reference voltage on both units and trim it to 2500 mV.
h) Check COMM ports. COMM port 2 recommended.
i) Connect a voltage source (pot giving out any voltage, 1250 mV preferred – in the example 637 mV) to one or all of Slave inputs.
j) Upload sketches and check auto opening of Serial Monitors (ERW 1.0.5 only).
k) If Serial Monitor does not open, check “preferences” on ERW.
l) Check Baud rate on Serial Monitors: must be 115200.
m) “Autoclear” must be on on both Serial Monitors.
n) At opening , Master on Serial monitor looks as SCREEN 1M. Now enter desired parameters in the Master sketch: k, t & restLvl. Re-load the sketch.
o) At opening , Serial Monitor may be blank or show SCREEN 2S, depends on speed of laptop.
p) Write “a” on Master Serial Monitor: it will show SCREEN 3M, Slave will briefly show “SLAVE RESET – SYSTEM ST-BY”, then go back to SCREEN 2S. System is now ready.
q) Write “b” on Master Serial Monitor and System will start operation, as per SCREENS 4M & 5S.
r) For 1250 V input Slave and Master will show “127” for 1250 mv input, in our example it shows “65”, for 637 mV input.
System is now operative and you can carry on checking the PWM output and the analogue output after the RC filters.
As many readers probably noticed, the described System was developed using Picoscope software, with a Picoscope 2000 series unit and Picolog software, with Picolog 1012 and DrDAQ Data Loggers. This instrumentation, plus a precision digital Multimeter, was all that was needed, forming a fully fledged Electronics Lab, to complete a relatively complex project.
