Zares ZTrak, User Manual

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© Copyright 2007 - ZARES (ZL1CVD Amateur Radio Equipm ent Supplies) – all rights reserved
Page 11
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ZTrak operates on 6.7 to 35 volts DC. An onboard voltage divider consisting of R11 & R7 is used to measure input
voltage however the reported range is limited to 6.7 to 15 volts.
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Power may be supplied at three points on the ZTrak board. Most often, it is supplied through pin 7 of the radio
connector. It may also be supplied through pin 9 of the expansion header. In addition, if a jumper is installed between
pins 9 and 10 of the expansion header, power may be supplied through pin 4 of the data connector.
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Make sure the squelch level is set correctly. If it is set too light, the ZTrak will detect the static as a carrier and think
another station is transmitting and will not send the packet. Set too strong and you run the risk of doubling with a
weaker station on the same frequency.
Theory of Operation
The heart of the ZTrak OpenTracker is a Freescale MC908KX8 microcontroller unit (MCU). The MCU contains 192
bytesof RAM and roughly 8 kilobytes of Flash program memory. It runs at a clock speed of 7.3728MHz.
U2 is a linear voltage regulator that provides regulated 5 VDC power to the circuit, and optionally to an external device
connected to Vext. C1 and C2 are the input and output filter capacitors, respectively.
Y1, C6, C7, and R10 form the clock oscillator circuit. The oscillator frequency of 29.4912MHz is divided by four in the
MCU’s clock module to produce the bus clock signal.
Audio output originates at pin 13 of the MCU. This pin is configured as a timer channel output and generates a pulse-
width modulated signal between 0 and 5 volts. Audio tones are generated in software using a sine wave lookup table. R2
and R8 limit the audio output level, and C2 couples the AC component of the signal to the audio output at radio port pin 1.
Pin 15 of the MCU produces the PTT output signal. It switches Q3, pulling the audio output down through R3 for handheld
PTT, and pulling radio port pin 3 to ground for other radios.
An externally applied PTT signal on the radio port pin 8 will pull the PTT output low through D2, and will pull pin 14 of the
MCU low (it is normally held high by an internal pull-up resistor) through D3.
The audio input from the radio is AC-coupled by C3 and biased by R9. R9 sets the carrier detect threshold. Radio port Pin
2 provides a DC-coupled input for radios with a squelch or carrier operated relay output.
R5, R1, and Q4 form an inverter/buffer circuit for the RS-232 input. The RS-232 output polarity is controlled in software.
The output level swings between 0 and 5 volts, and may not be compatible with all RS-232 devices.
U3 is a temperature sensor with an output of 10 mV per Kelvin. R6 limits its input current, and its output drives one of the
analog inputs on the MCU.
R7 and R11 form a voltage divider, the output of which is one third of the supply voltage. This voltage drives another
analog input on the MCU.
The LED is driven by a high-current output line from the MCU, through current limiting resistor R4. Lowering the value of
R4 will increase the brightness of the LED.