After visiting some web pages about 2.4 GHz ISM band spectrum analyzers based on the CYWM6935 module, I tried to build my own analyzer, but with some improvements. The references I found on the net used the parallel port or a serial link to a host computer. I want the analyzer to be portable, and easy to transport, so I will use a microcontroller and a graphical LCD.
I had also some old Nokia phones, so maybe I can use phone plastic box and build in LCD to make my own portable analyzer, but… Does it can be done? Let’s see:
Microcontroller: The microcontroller would be an ATMega8 running at 3.3 volts because both the the LCD module and the CYWM6935 are 3.3 volts devices. The ATMega8 will do nicely the job even running with low internal clock rates, so I choose to run it at 4 MHz using the internal oscillator.
LCD: The LCD would be the one from the phone, in this case a Nokia 3410. The LCD uses a PCD8544, so it must be easy to work with it. There are many code around to use this kind of LCD controllers
Battery: This phones can use two kind of batteries: Li-ion and Ni-Mh, but both types are equivalent from the equipment’s point of view. Useful voltage range is 4.2 down to 3.6 volts. My first idea was to use a voltage regulator to 3.3 volts, but I didn´t find a suitable one, so I choose to put a single 1N4004 diode between the battery and the circuit. The useful range (4.2 town to 3.6 volts) minus the 0.6 volts drop out at the diode will be seen as 3.6 down to 3.0 volts at the circuit supply. The LCD and CYWM6935 module can work from 2.7 up to 3.6 volts, so everything must work safely.
The prototype
I mounted a prototype to test module and microntroller functions when I found my first problem. According to the info on Internet, Nokia’s 3410 LCD uses a PCD8544 controller, the same as the Nokia 3310 LCD, so both LCD can be driven with the same firmware. Yes and no. Both LCD use the same PCD8544 instructions set, but screen resolutions are different. Original Nokia 3310 LCD is 84 x 48 pixels, but Nokia’s 3410 LCD is 96 x 65 pixels, so LCD routines must be rewritten to use the new resolution.
After rewriting the routines, you must expect a working LCD, isn’t it? Not again. The Nokia 3410 LCD have a visible resolution of 96 x 65 pixels, but the real resolution inside the LCD controller is 102 x 72 pixels, so you must to have this in mind while writing your code.
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