This is the simple Home page of my ongoing PPM projects.
Last update: 22-June-08
These are the links to the main description documents:
Ø 2005
1. 4/1/2005 : First Time Publication on MAG forum.
2. 17/1/2005--> Gradiomater Project Version 1.0 : Solid-state polarization (as designed by Jim Koehler)
3. 25/2/2005--> Gradiomater Project Version 2.0 : Based on the latest revision (7) of the PPM from Jim Koehler. It is using a slightly improved polarization circuit and two pre-amp stages based on the excellent low-noise LM394 transistor pair. Jim implemented this very design on a small SMT board (pictured on his descriptive document) but I implemented exactly the same channel design in Thru-Hole technology to make it more accessible to amateur builders. Also, I used a small PIC controller for signal analysis (as in version 1) rather than the ATMEL controller of Jim.
4. 5/6/2005à Gradiometer Project Version 3 : The design version 1 of the channel board and its signal analysis programs is now working satisfactorily in single sensor mode. After having proven the design and working of the channel board, it was now time to revise the packaging of the whole system. The version 3 has the following goals:
a) Make the system more modular and more flexible in order to define several types of configurations using the same mix of modules and to re-use these modules in other projects.
b) Study the feasibility of a double magnetometer system (fixed and mobile stations linked with RF)
c) Review the packaging of the boards to ease their insertion into a standard box.
d) In summary, the version 3 has the following characteristics:
· The channel board is a stand-alone sub-system. It contains all the hardware and logic necessary to control and execute the polarization and measurement cycles. It now uses a more sophisticated PIC16F628 with all the digital lines necessary to control the polarization. It also contains its own voltage regulator and an embryo of RS232 link (no RS232 level converter) for its easy testing in connection with a PC. Its PCB dimensions and connectors stay the same as in version 1 and 2. The design of the pre-amp stage has been improved and should be tested to check if it actually gives a better SNR than the design of version 1. The comparator circuit has been modified to be able to test both an external comparator device (like the LM393) and the internal comparator function of the 16F628.
· The main control board has now been reduced to the same dimensions and connectors as the channel board. The I2C RAM has been suppressed as the communication between the channel board and the main board is made directly in I2C.
· A passive back-panel hosts the boards and provides the raw battery power and the I2C bus interconnecting them.
· An RF board has been designed to plug into the back-panel and to be configured either as an RF emitter (used on the mobile station) or an RF receiver (used on the fixed station). This board is equipped with intelligence as a 16F628 and connected to the I2C bus as well. As an added feature, it provides an embryo of RS232 (to be externally complemented with a MAX232 level converter) for testing purpose.
Ø 2006
1. Most of the first half-year was devoted to the design and implementation of a ground resistivity measurement instrument and a controller board common to the resistivity and the PPM instruments.
2. Double PPM Project :
· The channel board has been upgraded with an external ADC and a more powerful Microchip Micro-Controller. We have now designed, experimented and tested a much better signal processing algorithm than the simple zero-crossing counting/timing. This algorithm captures 4096 ADC points during the first 500msec after the end of polarization (1024 periods of the signal sine wave) and applies some FFT-like calculations on the resulting vector. This gives a noise-resistant value of signal frequency. Its resistance to spikes and pulses is even better. This is due to the fact that the algorithm uses analog points (4 analog values per signal period) while the zero-crossing method uses just timings (2 timings per signal period).
Ø 2007
1. Differential PPM Project:
· Most of the first half-year was devoted to the design, implementation and tests of the Differential PPM instrument based on the PPM channel board designed by Jim and implemented in SMD technology. We chose to use ready-made (and well-tested) prototyping boards as controller for the multiple versions of this project . The first selected CPU was from a prototyping board (see http://www.olimex.com/dev/lpc-h2138.html ) based on the Philips LPC2138 and produced by Olimex in Bulgaria but we have now chosen the more powerful LPC2148 base (see http://www.olimex.com/dev/lpc-p2148.html ).
· The version 9 of the PPM Channel boards is now working very well and has been used for several actual field surveys on an archaeological site.
· We are now building the version 10 of the PPM Channel boards with the following improvements:
1. Polarization Switching protection against short-circuit at the sensor level.
2. Amplifier stage with dynamically-programmable gain.
3. Bandpass Filter with dynamically-programmable center frequency and Q ratio.
2. 17/11/2007 :
· We have now two fully operational PPM systems, the so-called ‘Double PPM’ and the ‘Differential PPM’. Actually, they are both one instrument part of a double, differential PPM system. We currently use one instrument (the Double PPM) as fixed station and the other instrument (the Differential PPM) as mobile station. Actual surveys have been successfully conducted using this pair of instruments.
· The current work-in-progress is the experiments with the dynamically-programmable amplifier gain and filter features on the Differential PPM project.
3. 11/04/2008 :
·
We have now successfully terminated
our experiments with the dynamically-programmable amplifier gain and filter
features on the Differential PPM project.
·
The front-end board and its layout is
fully tested and ready for production.
·
We now concentrate on our own designed
controller board replacing both the Olimex proto board and the daughter board
riding it. This board will have the same dimensions as the front-end board and
both will be fixed together with a shield alu sheet in between. This sheet will
also be used to dissipate the heat generated by the main 5V voltage regulator.
·
This board will first be made in four
prototype units by a professional PCB manufacturer, then, we shall assemble
them ourselves and test them to check if the PCB layout is OK for production.
Finally, we shall be ready for real production in small series.
4. 22/06/2008 :
·
We have modified the outline of our
boards to fit in an existing box. This box was originally designed for a
sophisticated PI metal detector with metal discrimination and produced in
larger volume than needed for that project, thus, we recuperated its (costly)
design and moulds.
·
We have also decided to produce a
fully assembled instrument with its sensor configured for underground surveys.
·
This new packaging will also integrate
an optional internal GPS device on a separate board together with the SD-Card
socket.
·
Five sets of boards were produced by a
professional company and one set has been assembled and tested in lab. It is
now put under real test conditions using the existing home-made sensors.
Meanwhile, a first set of sensor coils are being wound by a professional
company.
· Table showing the main functional and packaging differences between our kits and systems
|
Features |
Double PPM Kit Project |
Differential PPM Kit Project |
Fully assembled PPM Instrument |
|
Micro-Controller Engine(s) |
Two PIC 18F452 |
NXP LPC2138 |
NXP LPC2138 |
|
Signal Processing principles |
FFT-based |
FFT-based |
FFT-based |
|
Grid Storage |
EEPROM (256Kbits) |
SD-Card (any from 128Mbytes) |
SD-Card (any from 128Mbytes) |
|
Real-Time Clock |
Yes |
Yes, battery protected |
Yes, battery protected |
|
Short-Circuit and Polarity Invertion Protection |
- |
YES |
YES |
|
Tuning adjustment mechanism |
DIP switch |
DIP switch |
DIP switch |
|
Amplifier Gain adjustment |
Manual (trimmer) |
Software-driven |
Software-driven |
|
Bandpass Filter f0 and Q adjustments |
Static, wide band |
Software-driven, auto-adjusting, narrow band |
Software-driven, auto-adjusting, narrow band |
|
GPS Option |
- |
Yes, external GPS |
Yes, internal GPS option |
|
Packaging Technology |
Two Thru-Hole boards + back-panel |
Three SMD boards |
Three SMD boards |
|
Sensor |
To be provided |
To be provided |
Integrated |
|
Box (+ LCD, keyboard, buzzer, connectors) |
To be provided, LCD 16x2 |
To be provided, LCD 16x4 |
Integrated, LCD 16x4, waterproof membrane keyboard |
|
Main Battery |
To be provided |
To be provided |
Integrated, belt-attached, non-magnetic |
|
Post-Processing and Plotting |
Yes |
Yes |
Yes |
|
Carrying stick |
- |
- |
Yes, non-magnetic |
Any Comments and Questions are welcome at: w.bayot@skynet.be
Willy Bayot