Global Specialties ARX-MSP User manual

ARX-MSP
Minesweeper Kit
99 Washington Street
Melrose, MA 02176
800.517.8431
TestEquipmentDepot.com

1 Basic description of the design
The minesweeper extension will enable the ASURO robot to detect metallic objects underneath the
halved Ping-pong ball-glider. This will allow you – of course within the scope of the robot's and the
kit's possibilities - to develop the scenario of a robotic mine detector respectively treasury hunter or
a simplified version of a detector and tracer for cables, reinforcing bars and I-beams.
To avoid abundant explanations for the physical theories for magnetic fields and complex AC-
currents, the following chapters strictly document the basic description of the design and the user's
manual.
An operational amplifier (Opamp) has been applied to stimulate oscillations in the resonant circuit
consisting of a capacitor (C) and an inductor (L) applying an open pot core. Application of the
magnetically open pot core allows the magnetic field to expand into the surrounding free field and
to be influenced by neighbouring metallic objects.
Fig. 1 displays the schematic diagram. The resonant circuit consists of inductance L1 and capacitor
C1. The design allows resonant behaviour by cyclically exchanging the capacitor's electric field
energy and the inductor's magnetic field energy. The design's transfer frequency depends on the
values for the capacitor and for the inductor. Assuming negligible losses, the resonator's frequency
may be calculated by the following formula:
f0=1


L C
Exchanging the capacitor's electric field energy and the inductor's magnetic field energy cannot be
performed without losses and the losses will cause the oscillation to decay within a few cycles. We
continually have to feed energy into the system to compensate losses. In analogy to a children's
swing, the system will have to apply the correct phase in feeding the energy into the circuit.
Figure 1: Schematics for the "Minesweeper"-Extension

To achieve this goal, the design controls the capacitor's current proportionally to the capacitor's
voltage.
In this system the active element is the operational amplifier IC1A in a non-inverting amplifier
circuit with resistor R and the trimmer resistor TR1. This circuit will amplify the capacitor's
voltage at an adjustable rate of 1 up to 3, which will increase the current into resistor R1
proportionally to the voltage at C1. The losses in the resonator circuit may vary and to compensate a
range of tolerances, we will need an adjustable amplifier.
The operational amplifier IC1B is used as a comparator and compares the resonator's voltage with a
reference voltage of approx. 0.5V (depending on ASURO's battery voltage). The comparator's result
is applied to the extension pin INT1. To avoid signal collisions between the processor pin and the
output of the operational amplifier in a non-programmed processor, the port is being protected by
resistor R4. D4 replaces the previous line follower LED.
The left part of the circuit, containing a number of diodes and capacitors, generates a negative
voltage with respect to the ground level. The design will need a negative voltage as the resonator's
voltage swings in a positive and negative range, centred at the ground level.
Several types of designs are available for metal detectors. The ASURO design supports the
following two design types:
1. The design's amplification factor and the equivalent energy input for the resonator is to be
controlled at a level, in which electrical losses in the resonator are exactly to be
compensated as long as no metal is to be located near the coil. If metal objects are located
near the coil, the so-called eddy currents (for conducting materials) or demagneti ing losses
(for non-conducting, but ferromagnetic materials) result in extra losses, which will cause the
decay of oscillations.
. The design's amplification factor is to be controlled at a level, at which additional losses by
metals in the vicinity of the coil will be compensated and the circuit is to measure the
oscillator's frequency. In this mode any conducting materials near the coil result in eddy
currents, decreasing the field strength and the inductance and simultaneously raising the
oscillator's frequency. Ferromagnetic materials will increase the field strength and the
inductance, which will lower the oscillator's frequency. Additionally to detecting metals, this
design mode also allows a rather crude determination of the type of detected metal.
2 Constructional details
2.1 Manufacturing the coil
In case the coil has been prefabricated completely, including glueing the capacitor and applying the
cables as documented in fig. 8, you may skip this chapter. Otherwise you will enjoy the next steps!
First of all, we must apply 400 windings (yes, you are reading this correctly!) of very thin isolated
copper-wire (diameter 0.1mm) to a coil-carrier.
The kit supplies a double-sided coil-carrier for two core-halves (see fig. ).
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Figure 2: coil-carrier, complete Figure 3: coil-carrier, halved
In order to fit for our purposes, we will have to split up the carrier with a saw. A suitable saw for
this is a fine-tooth hacksaw. We will have to remove one chamber by sawing the other chamber in
the middle. This procedure results in a singular coil-carrier. Remaining sawing edges can be
removed with fine sandpaper (grain size: 40 or 300) or by carefully using a sharp knife (protect
your fingers!). The removed parts will not be needed and can be thrown away.
In order to apply the coil to the carrier, we suggest to place the carrier to a pencil-shaft or (even
better for it's conical form) to a suitable paintbrush. In an optimal method we also carefully fix a
few centimetres of the isolated copper wire together with the carrier at the pencil's shaft as
demonstrated in fig. 4. As an extra fixation you may use some adhesive tape (cello tape) to avoid
slipping movements of the wire.
Figure 4: Winding preparations
After these preparations, you carefully start winding up the 400 turns of wire. Of course you avoid
reversing the winding direction and you fill the windings neatly, otherwise the 400 windings of wire
will fail to fit in the available place. In case the wire should break (there is no room for a repair) or
you fail to count correctly, you must restart the procedure. No problems are to be expected for
winding numbers between 380 up to 4 0, but do not exceed these tolerances.
Having completed the windings you are advised to fix the windings with some nail varnish or
instant glue. As soon as the glue has hardened you may carefully remove the cello tape and the
pencil or brush.

You may also cut the wire, but do not forget to reserve a few centimetres at both sides. The wire-
endings have to be directed into one direction and are not allowed to pass through the hole in the
coil-carrier (see fig. 5).
Fig. 5: coil-carrier - completed
Having completed the coil-carrier, you can fix the structure into the core with some instant glue.
The wire's endings are to leave the core at the closed core-side through a slit (see fig. 6).
Fig. 6: Coil - fixed in the core
At this stage you have to remove the isolation at the wire-endings, starting at one or two
millimetres from the core towards the outside. The optimal tool to remove isolation is a soldering
tool with some fresh solder at the soldering tip. Apply the heated top for some time until the
isolation has been removed and a thin layer of soldering tin is covering the wire. Warning: the
generated smoke may cause damage to your health and should not be inhaled!
At last you put some instant glue to the backside of the coil and fix the 10nF-capacitor (imprinted
text: 103) in a suitable position to point the wiring connections towards the slit for the coil-
windings. Fig. 7 demonstrates a location for the capacitor besides the carrier's hole – just in case we
may need the hole for some other purpose. The published design however does not really require
this exact position.
Now cut the capacitor's wiring connections to approx. 5 mm, wind the tinned copper wire-endings
around these wiring connections (maybe using a pair of tweezers) and fix the connection by
soldering.
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Fig. 7: Coil with capacitor
Next, we proceed with the ready-made cables. The dual cable has been dimensioned at 70 mm,
stripped, twined and tinned at the cable-endings. Solder the cable-endings directly entwined to the
capacitor-endings with the endings and pointing in the same direction as shown in fig. 8. Polarity is
irrelevant. If you have a multimeter you may now measure the resistance between both cable-
endings. The resistance-value is to be approx. 30Ω. If the value exceeds 60Ω you should check the
proper removal of the isolation layer at the thin copper wires, the soldering quality and any ruptures
of the soldering and cables. Should the resistance-value be much lower (< 10Ω), you must check for
short circuits at or near the soldering area. Unfortunately you are unable to detect short circuits
within the winding area.
Fig. 8: Coil (assembly completed)
2.2 Inserting the coil assembly
To insert the completed coil assembly into the robot, you start by removing the ping-pong ball.
Right now you will be grateful if you have glued the ping-pong ball at a minimal number of points
instead of an overall glued area of the component.
Proceed by glueing – again using an instant glue – the coil at the backside under the ping-pong ball
(see fig. 9).

Attention: If ASURO has not been prepared for assembling an extension PC-board, you will have to
postpone attaching the ping-pong ball until the preparation for the extension board has been
completed.
Fig. 9: Coil - attached to the ping-pong ball
2.3 Inserting the extended plug sockets
Before assembling the components to the PC-board you will have to insert the extended plug
sockets. You will have to use a different procedure depending on the status of the ASURO-system.
Please check whether the ASURO has been prepared for assembling an extension PC-board or not.
a) AS RO does not provide extended plug sockets for the extension board
In this case you will have to remove the components for the line-tracing (the photo-transistors T9
and T10, as well as the LED D11) from the PC-board. These activities require a removal of the
ping-pong ball. The easiest way to proceed is to heat the components, which are to be removed with
a soldering device while simultaneously and carefully pulling the components out of the PC-board's
holes. If you are lucky the PCB-holes are free, otherwise the superfluous solder may carefully be
removed with a solder sucker and / or a solder wick.
Now the two- and three-poled male and female plug elements have to be assembled and –
additionally to the plugs at the ASURO-board – inserted in the ASURO-PCB as illustrated in fig.
10. In a following step you first insert the extension board and at last solder the male and female
plug elements at the extension-board and the ASURO-main PC-board.
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Fig. 10: Inserting the Extension-PCB
b) AS RO already provides extended plug sockets for the extension board
The two- and three-poled plug elements are to be inserted into the plugs at the ASURO-PC-board
(see fig. 10), on top of which you attach the extension board. The pins will be protruding from the
PCB. If all components are well-placed, the extended plug sockets are to be soldered to the
extension board.
2.4 Placing the ping-pong ball
Having soldered the extended plug-sockets to the printed circuit board, you have to unplug the
extension board and place the component apart for further assembling activities. Now pull the
connecting cable of the coil through the hole in the ASURO-PCB and attach the ping-pong ball
(together with the included coil) carefully with merely three or four glueing dots at the ASURO-
PCB.
Fig. 11: Extension board with extended
plug sockets

2.5 Assembling the Printed Circuit Board
After placement of the extended plug sockets (and eventually the plug arrays as well), you may
remove the PCB and complete the assembly phase. According to the component placement drawing
(see fig. 1 ) you are advised to proceed the following way: Up to R7 all resistors are to be placed
upright – according to the ASURO-standard, which implies bending a U-turn (180° ) for one leg of
the components. Bend both legs for component R7 at an angle of 90°.
Fig. 12: Component placement drawing
Please insert the components in the following sequence:
IC1: Initially merely insert the socket, be careful to apply the correct polarity!
D1, D2, D3: 1N4148, be careful to apply the correct polarity!
C4, C5, C6: 100nF ceramic
R1, R2, R3, R7: 10kΩ 5% (brown, black, orange, gold)
R4: 0Ω 5% (red, red, brown, gold)
R5: 1kΩ 5% (brown, black, red, gold)
R6: 100kΩ 5% (brown, black, yellow, gold)
C2, C3: Electrolytic capacitor 100µF, minimal 16V, be careful to apply the correct polarity!
TR1: Spindle-trimmer 0k upright
D4: LED 5mm rot, be careful to apply the correct polarity!
CON1: screw terminal, cable entry must point to the PCB-edge.
IC1: Now insert the TS91 into the socket. Maybe you will have to bend the legs slightly. Be
careful to apply the correct polarity: the marker at the component must be oriented to the
corresponding marker at the socket!
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Fig. 13: Completed and placed Extension Board
Note: Initially the terminals VCCOUT1/ , GNDOUT1/ and ADC OUT/ADC3OUT will not be
needed. Additionally to the fixing hole at the PCB, these terminals may later be used to connect two
distance sensors in a triangulation-sensor-system. This will allow the ASURO to apply an
autonomous navigation system and to be searching metallic objects as well.
For more details please consult “More Fun with ASURO, Volume II”. Instead of attaching the
triangulation-sensors directly to the ASURO-PCB, you will now have to attach these to the
extension board.
2.6 Startup procedure
Having attached the ping-pong ball including the coil and having completed the PCB-assembly, you
can now insert the PCB into the (deactivated!) robot. Please check the isolation of the components
carefully: none of the components at the ASURO-PCB are to short-circuit the metallic areas of the
extension board. The coil cabling is to be guided from below the PCB to the side of the screw
terminal CON1 and may now be attached to the screw terminal. In this case the polarity may be
neglected.
In order to view the oscillations in the resonator circuit, you enter the following program
(MinesweeperTest1):
#include "asuro.h"
extern volatile unsigned char count72kHz;
int main(void)
{
unsigned char oscillation;
Init();
R &= ~(1<<2); // Change Port Pin 2 to input
StatusLE (OFF);
while(1)
{
count72kHz=0;
oscillation = FALSE;

while (count72kHz<100) {
// etect low level
if ((PIN & (1<<2)) == 0) oscillation = TRUE;
}
// If oscillator is running, no metal object is within
// range, so LE should be off
if (oscillation) FrontLE (OFF); else FrontLE (ON);
}
return 0;
}
This program will switch off the LED as soon as the oscillator is working.
Depending on the activated detection method (decay mode of the oscillations respectively variations
of the oscillator frequency), we will need different calibration methods. At first we will explain the
calibration for the decay mode of the oscillations. This simpler method should always be preferred
for testing the system (with the previously referenced program).
If the red LED at the extension board is not activated after switching on the system, please turn the
spindle trimmer clockwise until the LED is activated. The trimmer may be turned ten rotations
clockwise, respectively counter-clockwise and will not be damaged if you exceed the operating
area. If turning over ten rotations does not effect the system we will have to proceed with the
debugging phase...
After a successful calibration please place the robot on top of a definitely non-metallic location (on
top of a plastic or wooden box, respectively on a table without nails or screws...) and turn the
trimmer counter-clockwise until the LED extinguishes. You may have to repeat the calibration
procedure again, as temperature drifts and changing battery levels are influencing the operation-
point of the system. Careful calibrations will increase the sensitivity of the system but will also
reduce the intervals between re-calibrations.
As soon as you near the ping-pong ball with a metallic object (e.g. a screwdriver), the LED should
be activated – at least the moment you touch the system.
The sensor will now be sensitive enough to detect even small pieces of aluminium foil at the
backside of a paper board.
In order to monitor the frequency variations you should start by calibrating the sensor in the exact
application mode. In this mode the robot is to be placed in a position for the maximal level of the
expected sensor signal (e.g. very close to the metallic object). Then turn the trimmer counter-
clockwise as long as the LED is activated. Now you may use the following program for
demonstration purposes (MinesweeperTest ):
#include "asuro.h"
#include <stdio.h>
extern volatile unsigned char count72kHz;
int main(void)
{
unsigned char oldlevel=0, newlevel;
unsigned int freq;
int i;
char s[9];
Init();
R &= ~(1<<2); // Change Port Pin 2 to input
StatusLE (OFF);

while(1)
{
freq=0;
for (i=0; i<100; i++) {
count72kHz=0; // This counter is incremented in timer interrupt
FrontLE (OFF);
while (count72kHz<72) {
// etect level change
newlevel = PIN & (1<<2);
if (oldlevel != newlevel) {
oldlevel = newlevel;
freq++;
FrontLE (ON);
}
}
}
sprintf(s,"%5d\n\r",freq);
SerWrite(s,7);
}
return 0;
}
2.7 The debugging procedure
If the system does not work as expected, we will have to start the debugging procedure.
Unfortunately we cannot provide as many debugging options as for the basic ASURO-system. The
use of a multimeter may help to debug the system.
●Please start by checking the correct compilation of the test program. Has the program really
been flashed? Proceed by checking the soldering locations and the polarities and values for
the components.
●Check the connections of the coil system for correct removing of the isolations and applying
the solder. Did you really remove the isolation? At a deactivated (!) robot you should be able
to monitor a resistance of 30Ω at the terminals for the coil.
At much higher measured resistor values, the cable has not been connected correctly, some
isolation at the copper cable has not been removed properly – preventing good conductivity
- or the thin copper wire of the coil has been disrupted at the assembly phase. The last
problem often occurs in the neighbourhood of the capacitor.
At much lower measured resistor values, you may locate a short circuit at the printed circuit
board or in the coil. You are now advised to remove the cable from the screw terminal and to
repeat the measurement of the resistance value at the screw terminal. If the resistance is
much higher than 30 Ohms, you may locate the short circuit area at the coil module.
●At an activated robot you should be able to monitor an operating voltage in the range 4.5 ..
5.5V between the terminals GNDOUT1 and VCCOUT1. If the operating voltage does not
meet these specifications the battery may be empty, the robot may be deactivated, the
connections for the battery compartment may be interrupted or a cold soldering point occurs
in the neighbourhood of the rear extended plugs at the extension board or the robot itself.
●The voltage for the operational amplifier may be monitored between pin 4 (minus) (at the
bottom left side if the mark at the IC is at the topside) and pin 8 (plus) (at the top right side).
The voltage should be at least V higher than the battery voltage.
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