(latest version 3.8)
project was designed to see how much could be done with a PIC chip and
just a few parts. The image at the right shows the capacitance measuring
If you have produced one
of these, please send me a photo and I will add it to the Superprobe
Hall of Fame Page.
Superprobes are also available
for sale - but not from us. Check out these sources.
This device is designed around a PIC16F870,
a 4 digit LED display module and very little else. Note: I have received
a lot of inquiries on this project. To date, several have been duplicated
world-wide. Many have been constructed in other types of cases.
As long as the circuit is wired as shown, and the object code (below)
is programmed into the PIC, the devices all worked perfectly.
I get a lot of requests for translating
the source file for MPASM. I have received this file
from someone who converted it - supmp.asm.
The LTC4627 display is sold by Mouser as
512-MSQC4911C for $2.50 in single quantity. (Note: Mouser is no longer
carrying this device - you can currently find one at Digi_key )
The LM2931 is a low drop out regulator
also sold by Mouser (24 cents). The regulator allows the unit
to operate on 5 volts or as much a 30 volts. It also provides 30
volts of reverse polarity protection.
As you can see in the schematic
even the usual resistors associated with driving the display have been
eliminated. Usually, separate resistors need to be used in series
with each segment drive in order to evenly drive the display.
The PIC chip, however, limits the current flow to about 25 ma per line.
The software is written in such a way that only one segment is active
at any one time. This eliminates the effect of multiple segments
having to share the same current source at the same time and dimming some
digits more than others.
Various testing modes use the resistors
in different ways. Unused resistors for any particular mode are
removed from the circuit by having their pic pins floated. R5, for
instance, is used for the logic pulser function. R4 is used to charge
a capacitor to measure its value.
unit was built into a case from a scrapped Radio Shack logic probe (sold
for $8 at a closeout price). Similar cases can be found if you look
around a bit. I have recently ordered some form Kelvin
as part #430068 for $3.75 each.
All of the original electronics were removed
and one side was cutout for a piece of transparent red Plexiglass.
The circuit was built up on pad-per-hole pref board.
Operation is via 2 pushbuttons. Holding down button
#2 while pushing button #1 cycles through operating modes.....
Prob PULS FrEq Cnt VoLt diod
CaP CoiL SIG ntSC 9600 Midi
r/c  Prn ir38 PWM StOP
(Done on the 7 segment displays).
Here are how each
of the modes work at present....
||The logic probe shows 'H' for high (over 3.7 volts), 'L'
for low (below 0.8 volts) and '-' for floating in the first display
location. If a pulse is detected (0.5 usec minimum), the second
location flashes a 'P'.
||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.
||In the frequency counter mode, hitting 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 42,345,678 hz is displayed
as 42.34 with a flashing decimal. Holding down button #1 in
this case will display 5678.
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.
||The voltmeter uses the power going into the probe as a
voltage reference. The current implementation shows only an
approximate voltage - about 2% high. This can still be very
useful for most measurements. Do not connect the probe to voltages
that exceed 5 volts under any conditions.
||Diode Junction Voltage
||This is just the voltmeter function with 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
||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 to about 500 uf are displayed. The larger the capacitor,
the longer it takes to measure. A value of 100uf takes a couple
||When an inductor is connected from the tip to the ground
lead, and button #1 is pushed, its value is displayed. Values
from 0.1 to 999.9 millihenries are displayed. Note:
this function assumes that 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.
||This mode generates a 500hz square wave at about 0.5 volts.
The signal is only generated while button #1 is held down.
||Generates an NTSC video frame with a white dot pattern.
||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 other polarity is done. New
feature: Button #2 cycles thru 1200, 2400, 4800, 9600 baud.
||Sends note number 60 (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.
||Generates 1ms to 2ms pulse for r/c servos. Button
1 increases pulse, Button 2 decreases pulse. Defaults to 1.5
ms each time mode is entered.
||Generates 1 - 9999 hz square wave. Button 1 decreases
frequency, Button 2 increases frequency.
||Pseudo Random Number
||Generates 10khz digital PRN series.
|Generates 1 millisecond on and 2.5 millisecond off of 38khz
square wave. When connected to IR LED, used for testing IR receiver
|Generates variable pulse width 3-97 percent of a 6khz (approx)
digital signal. Button 1 decreases pulse width, Button 2 increases
1 starts/stops timer. Change of state on probe tip also will start/stop
timer. Button 2 resets timer. Timer counts
in 1/100 seconds from 0-99 seconds, then counts in 1/10 seconds from
100-999 seconds, then counts in whole seconds from 1000-9999 seconds
(about 2 hours 46 minutes).
In any mode, holding down both buttons exits to the menu.
Once there, releasing and pressing button #1 cycles thru its modes forward.
New Feature: Button #2 cycles thru modes backwards.
The mode is saved on power down. Since this device
takes its power from the circuit being tested, powering down and back
up will restore the same operating mode.
Any other suggestions for this project? See email
address on home page.