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Optoelectronics
Miniature recording frequency counter
MicroCounter is a miniature recording frequency counter in the shape of
a pager,
introduced in 1997 by
Optoelectronics in Fort Lauderdale (FL, USA).
It is part of a the Techtoyz series,
all of which are housed in the same plastic
Motorola Basic Bravo 1 pager enclosure.
The device can be used to quickly determine the frequency of a nearby
transmitter in the 10 MHz to 1.2 GHz range.
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Pagers were popular devices at the time the Optoelectronics
MicroCounter was introduced, mainly resulting from the preceeding decade
in which GSM (2G) mobile telephony was not yet
available and analogue (1G) mobile telephony was
very expensive and not widely spread.
This allowed anyone to carry the device without attracting attention,
and covertly register the frequency of any nearby radio transmission.
The MicroCounter automatically stores up to three frequencies in
its memory.
A padlock symbol is shown on the display when memory is full.
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The MicroCounter is part of a series of three devices that became known as the
Techtoyz, the other two being an RF detector
and a DTMF tone decoder. All these devices were housed in the same plastic
enclosure, which had probably been obtained – together with the 12-segment
LCD – from Motorola after production of its
Basic Bravo pager had ended. Although the MicroCounter works exceptionally well
and was relatively inexpensive, it was criticized by some reviewers for its lack
of storage capacity. The slightly larger Scout Model 40 – introduced 2
years earlier – might have been a better alternative as it offers 400 memory
positions, albeit at a much higher price.
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The Basic Bravo pager was also sold by Motorola as an OEM product,
as a result of which it can be found under a variety of brand names.
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The image below provides an overview of the features of the MicroCounter.
The device is powered by a single 1.5V AA-size battery, which should
last for 12 to 15 hours. At the left side (when viewed from the top)
is a three-position slide switch that is used to select the mode of operation.
It has an integrated push-button that allows selection of sub-modes.
Just below the mode switch is a 2 mm jack socket for connection of
an external antenna, which was available separately.
At the top of the device is a 12-digit Liquid Crystal Display (LCD)
that shows the current or recorded frequency. At the front are two push-buttons:
a grey one with a ↑ symbol and an unmarked black one. Both buttons
have the same function, which depends on the currently selected mode.
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| Switch | Mode | Description |
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| Up | NORMAL | Shows running frequency for as long transmission continues.
Press ↑ to alter gate time: 1 KHz, 100 Hz, 10 Hz. |
| • Press 1 × | FILTER | Shows last detected frequency until new one is encountered.
Press ↑ to alter gate time: 1 KHz, 100 Hz, 10 Hz. |
| • Press 2 × | CAPTURE | Up to three frequencies are logged (until memory is full).
In this mode, only 1 kHz gate time is available. |
| Middle | RECALL | In this mode, previously recorded frequencies can be read.
Use ↑ to scroll through captured frequencies. |
| Down | OFF | Device is off. |
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The device can capture up to three frequencies in its memory. When the
memory is full, a padlock pictogram is displayed on the LCD and no
further frequencies will be logged. To clear the three memory positions,
hold the ↑ button while turning the device ON.
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The device is housed in a molded plastic case that consists of
two shells, held together by two Allen head screws at the rear.
The interior can be accessed by removing these two
screws, after which the rear case half can be removed.
This exposes the interior as shown in the image above.
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Inside the device are two printed circuit boards (PCBs), interconnected
by an 8-pin header. The lower board (i.e. the larger one) is a universal
base board that holds the battery contacts, the MODE selector and
the LCD. At the bottom side (shown on the right) is a DC/DC
converter, a microcontroller, an EEPROM and a LCD driver.
The DC/DC converter [a] is a Linear Technology LT1307, which
converts the 1.5V battery voltage to 3.3V for the digital circuits.
The 8-bit microcontroller [b] is a COP8SAC720M9 with 4KB OTP,
128 bytes of RAM and a Microwire 1 interface.
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Note that this is a universal board that was also used in the other
devices of the Techtoyz family (RF detector & DTMF decoder),
albeit with different firmware.
The data bus of the microcontroller is connected a Philips PCF8576CT universal LCD
driver [c] that drives the Motorola pager display.
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The I2C bus of the microcontroller is connected to a Catalyst Semiconductor 2
128-byte 24C01 EEPROM [d] for storing the captured frequencies.
A separate SPI bus is brought out to the 8-pin expansion connector on which the
feature board is fitted. This board — shown in the image on the right —
is specific for the MicroCounter and is built around a Xilinx CX3430
Spartan 3 Field-Programmable Gate Array (FPGA) [e].
The antenna signal is first amplified in a two-stage amplifier with BFR505
wideband transistors (N30) [f] and then passed to an UPB587 prescaler [g].
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The prescaler divides the frequency by eight before applying the signal to the
FPGA, where it is further processed. The FPGA effectively implements the
complete frequency counter in firmware. When the device is switch ON, it displays
the text 'OPTO' whilst the firmware
is transferred via the SPI interface from the microcontroller on the base board
to the FPGA on the feature board.
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Microwire is the National Semiconductor variant of the Philips I2C standard.
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Catalyst Semiconductor, Inc. (CSI) is the original inventor and patent holder
of the EEPROM.
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Device Recording frequency counter Purpose Covert frequency capturing of near-field transmissions Family Techtoyz Model MicroCounter Manufacturer Optoelectronics Country USA Year 1997 Frequency 10 MHz - 1.2 GHz Resolution 1 kHz, 100 Hz, 10 Hz Impedance 50Ω Input ≤ +15 dBm (50 mW) Sensitivity < 5 mV @ 150 MHz Time base 10 MHz Gate 3 selectable gate times Memory 3 Display 12 digit LCD Antenna TMC-100 (rubber duck) Power 1.5V (AA-size battery) Duration 15 hrs (with alkaline battery) Dimensions 73 × 50 × 32 mm Weight 70 g (with battery) Price USD 99 (1998), antenna USD 9
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- RF Detector
- DTMF Decoder
- Micro Counter
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- LT1307, Single Cell Micropower 600 kHz PWM DC/DC Converter
Linear Technology Corporation, 1995. Rev. A.
- COP8SA Family, 8-bit CMOS ROM based OTP Microcontroller
COP8SAC720M9, 4KB OTP, RAM 128 Byte, 20-pin SOIC.
National Semiductor, 1999.
- PCF8576CT, Universal LCD driver for low multiplex rates
NXP, 16 December 2013, Rev. 13.
- 24C01J, 1K (128 byte) 5.0V I2C Serial EEPROM
Microchip Technology Inc., 1997-2012.
- Spartan 3A FPGA (Xilinx XC3430A)
DS610. Xilinx, 4 October 2010.
- BFR505, NPN 9 GHz wideband transistor
NXP, 7 September 2011. Rev. 4.
- 1.0 GHz Divide-by-1/4/6 Prescaler
NEC, undated.
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© Crypto Museum. Created: Sunday 03 August 2025. Last changed: Monday, 04 August 2025 - 20:32 CET.
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