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SUPER PROBE MkII |
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This project
has been adapted and modified from a project designed by Luhan Monat of mondo-technology.com
The original project has been changed slightly with an added feature but
retaining the simplicity of the circuit
and the code. It just goes to show what can be done with a simple
microcontroller and a set of instructions.
This is by far the most complex project we have ever described and it
should be thoroughly investigated to see exactly how each function has
been designed and how the external components are "switched into
circuit" to charge and discharge the component being tested.
By looking at sites on the web you will see this has
been a very popular project but no-one has
provided a kit of components to build it. That's what we have
done.
We have added one extra feature (Voltage: 0 to 25v) and provided a pre-programmed PIC chip
and a complete kit of parts for a total of $18.00 plus postage.
The case is extra and can be purchased from one of the suppliers mentioned below.
The project is built on a Printed circuit board 22mm x 100mm and comes with a pre-programmed chip, surface mount components,
4-digit display,
5v6 zener diode, 20MHz Xtal,
regulator, switches, very fine solder, wire and battery clip. You would normally
need to go to more than 3 different suppliers and also get
someone to program the chip. We have done it all for you and
modified the program to reduce the flicker (the strobing effect
that separates the segments when the display is moved).
The project does an enormous number of things and you have to study the
list of functions to see how each function works and the features within
each function.
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To cycle through the 20 functions, turn the
Probe ON and the centre segment of the first display will
illuminate. |
If a pulse
(0.5us) is detected, the second
display flashes 'P'.
Here are the
details of the 20 functions:
Prob
Logic Probe
Logic Probe shows the first position
of the
display:
PULS
Logic Pulser
The
Logic Pulser shows the pulse rate (5, 50, 500, 5.0) in the last
3 locations. The first location shows the sensed logic level as
a dash in the bottom or top of the digit. When button #1 is
held down, a series of 0.5 microsecond pulses are generated in
the opposite direction and the center segment is lit. Pushing
button #2 cycles thru the 4 pulse rates. The selected pulse
rate is saved on power down.
FrEq
Frequency Counter
In
the Frequency Counter mode, pushing button #1 switches the
display to the next 4 digits of the count. For instance, the
display shows '12.57' for a frequency of 12,576 Hz. Holding
down button #1 shows '2576' - the lowest 4 digits. If a decimal
point shows, the value is in KHz, if the decimal is flashing,
the value is in MHz. Hence, a frequency of 42,345,678Hz is
displayed as 42.34 with a flashing decimal. Holding down button
#1 will display 5678.
Cnt
Event Counter
In
the event count mode, the display shows the lowest 4 digits.
Button #1 switches to the next higher 4 digits while held down.
Button #2 resets the count.
VoLL
Voltmeter
Switch the 5v_25v
switch to 5v. The
project uses the 5v from the regulator as a
reference. Do not connect the probe to voltages
above
5 volts.
VoLH
Voltmeter
Switch the 5v_25v
switch to 25v. The display measures voltage to 25v. Do not connect the probe to voltages
above 45 volts as the probe does not detect anything above 25v
and the components are not rated for high voltages. The 1M is
the "protection resistor." in the voltage divider.
diod
Diode Junction Voltage
This
is just the voltmeter function with a 10k resistor feeding current
to the probe tip. When a diode or transistor junction is
connected from the tip to the ground lead, the drop voltage is
displayed.
LEdS
LED
voltage drop
Measures the characteristic
voltage drop across a LED @3mA.
Ideal for detecting cathode lead and matching
LEDs.
(29-6-2011)
Approx 0.1v is dropped across 22R so take 0.1v
from LED reading.
LOW Battery is detected by open probes
reading less than 5.95v
Cap
Capacitance Measurement
READ THESE NOTES:
When
a capacitor is connected from the tip to the ground lead and
button #1 is pushed, its value is displayed. Values from .001 uf
(1n or 1,000p) to about 500 uf are displayed. The larger the capacitor, the
longer it takes to measure. A value of 100uf takes a couple of
seconds.
To do this, turn the Probe OFF. Fit the
electrolytic to the leads. Turn the Probe ON. It
will display CAP and then go blank while it
reads the value of capacitance. It will then
display the value.
Coil
Inductance Measurement
When
an inductor is connected from the tip to the ground lead and
button #1 is pushed, its value is displayed. Values from 0.1mH
(100nH)
to 999.9 millihenries are displayed. Note: this function
assumes the DC resistance is not more than a few ohms.
Also, if the unit gets 'stuck' in this mode, jumper the tip to
ground to free it.
SIG
Signal Generator
This
mode generates a 500Hz square wave at about 0.5 volts. The
signal is only generated while button #1 is held down.
ntSC
Video Pattern
Generates an NTSC video frame with a white dot pattern.
SEr
Serial Ascii
Each
time button 1 is pushed, the letters A-Z followed by cr/lf is
generated. Auto polarity sensing. If the signal injection
point is originally high, then normal (zero start bit) ascii is
generated. Otherwise, the opposite polarity is created. New feature:
Button #2 cycles thru 1200, 2400, 4800, 9600 baud.
Midi
Midi Note
Sends
note middle C on any of the 16 midi channels.
Holding button 1 sends 'note on'. Release of button 1 sends
'note off'. Button 2 cycles thru the 16 channels. The midi
channel number is stored.
R/C
R/C Servo
Generates 1mS to 2mS pulse for r/c servos. Button 1 increases
pulse, Button 2 decreases pulse. Defaults to 1.5mS each time
mode is entered.
_|¯|_|
Square Wave
Generates 1 - 9999 Hz Square Wave. Button 1 decreases
frequency, Button 2 increases frequency.
noiS
Pseudo Random Number
Generates 10kHz digital PRN series - commonly called :White
Noise."
ir38
IR LED
Generates 1 millisecond ON and 2.5 millisecond OFF - 38kHz
square wave. When connected to IR LED, used for testing IR
receiver modules.
PWM
Pulse
Width
Modulation
Generates variable pulse-width 3% to 97% of a 6kHz (approx)
digital signal. Button 1 decreases pulse-width, Button 2
increases pulse-width.
StOP
Stop Watch
Button 1 starts/stops timer.
Change of state on probe tip also will start/stop timer. Button
2 resets timer. Timer
counts in 1/100 second from 0-99 seconds, then counts in 1/10
second from 100 -999 seconds.
The original project is from Mondo Technology.
The case was a broken Logic Probe from Radio Shack - but see the
brightness of the display. It is perfectly viewable when each segment is
accessed individually. This is the way the display is accessed in the
program. It is a rather unusual way to scan the display but has two
features. It allows the outputs of the chip to be connected directly to
the display without putting too much strain on the FETs and
produces equal illumination for all segments. 
Here is the Super Probe from Heli:
Here is a Probe case "U-SONDA3" and tip.
"U-SONDA-tip," from
GM Electronic Slovakiaa: (cost: about
$3.00 USD including tip, plus postage):
Here is the Super Probe from:
http://ikon.wz.cz/mondo/sonda_2.php,
with the PC board and top-half-shell of the case: Here is a Logic Probe case from
Kelvin, for $3.75 plus postage, but they require a minimum $150 order!!
Here is a
Logic Probe case from
Rapid Electronics: It costs $10.50 plus postage.
The CIRCUIT
http://heli.xbot.es/SuperProbe/SuperProbe.htm
External size excluding tip (mm):145 x 30 x 21 Window size (mm):95 x 19
Order code:31-0330
Super Probe MkII Circuit
The circuit is very simple. It
uses a PIC 16F870 microcontroller connected directly to a 4 digit
display.
All the segments are connected together to reduce the wiring to 14 pins. No current limiting resistors have been used
between the micro and display and this means the
voltage-drop will be across the FETs inside the micro.
The display is illuminated ONE SEGMENT AT A TIME. And this means it
takes 4x7=28 to display all the segments (plus extra for the decimal
points). You would think the display
would be very dull. But this is not so. The display we have supplied in
the kit is "super-bright red" and although each segment is seeing only a duty
cycle of about 3-4%, the overall brightness is perfect.
During each segment illumination, we have one output of the chip driving
HIGH and one driving LOW. The LED drops 1.7v leaving 1.65v across
the top FET and 1.65v across the lower FET. This is overdriving the FETs
but thy do not seem to suffer.
The current taken by the project is 20-30mA. The rest of the components
are connected to the probe tip to create different charging and
discharging values for testing capacitors and inductors and for the 25v
voltage range.
The crystal needs 2 capacitors and the buttons need pull-up resistors (portB is the only port with weak pull-up resistors). The 249k is
created with a 220k and 33k in series. The 22p capacitors are created
with 2x47p caps in series and the kit contains 4x47p surface-mount.
The brightness of the
display is superb
Click HERE for larger image
Here is the Super Probe constructed by Ahyan Yilmaz of Kocaeli TURKEY:
Note: the link is now a track on the top side of the board. No
tracks need to be cut with the new PCB's
Surface-mount certainly makes a very neat project. The secret is the use of 0.8mm solder.
SURFACE-MOUNT COMPONENTS
We have used SM components to make the
project as small as possible.
They also make it look simpler as they "disappear" under the
board.
You will need fine tweezers to hold
them in place while one end is soldered to a pin of the 28 pin IC socket.
Using very fine solder (supplied in the kit) makes soldering easier and quicker. Always solder resistors with the value
showing.
CONSTRUCTION
This project is for medium-to-advanced constructors as
it is very compact. It is
built on a double-sided PCB and the kit comes with all parts, including a pre-programmed chip.
They are fitted
as shown in the photos above.
Two tracks need to be cut near the crystal and a link fitted under the board.
When the IC socket and display are fitted, they are soldered in place.
The next thing is fit the crystal, switches, regulator and then the
surface-mount components. Tin one pad then fit the surface-mount
component. Use fine tweezers. Now solder the other pad and the solder
will run under the chip. Don't forget to cut the two tracks next to the
crystal and join the track with a short length of enamelled wire. Fit
the regulator and short lengths of tinned copper wire in the holes for
the battery snap.
Twist the wires together and cut them short so they just fit through the
hole in the battery snap. Tin the wires and fit the battery snap and
solder the wires to the snap. Refer to the photo above to see how the
snap is connected.
