FM Radio Player for RTL2832U sticks

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USB TV sticks using RTL2832U chip are well known for their ability to send raw samples to USB host. This makes it possible to process various signals in software (SDR). There are many software tools for this purpose and most of them can demodulate also FM radio, with stereo and RDS support.

The problem is that these applications have full featured SDR abilities, with spectrum analysis and waterfall display. This makes them not at all lightweight. I've been looking quite hard for a simple FM radio player for my RTL-SDR dongle.

Some of the RTL2832U dongles come with FM capable player on the CD. Unfortunately not all. After some searching I was able to find a simple tool that demodulates FM stereo signal and displays RDS data. The application was most probably a test tool designed by Realtek to illustrate features of RTL2832U.
FM Radio Player for RL2832U sticks

CH341A Mini Programmer Schematic and Drivers

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CH341A is an USB interface chip that can emulate UART communication, standard parallel port interface, parallel communication and synchronous serial (I2C, SPI). The chip is manufactured by Chinese company Jiangsu QinHeng Ltd.

CH341A is used by some cheap memory programmers. The IC is somehow limited in this configuration, because the programmer makes use only of the SPI and I2C interface. A popular device is the so-called "CH341A MiniProgrammer" that you can buy for 2 to 5 USD.

The problem is that this device comes as-is, without any documentation or software. Drivers are available from manufacturer's website (but the site is written in Chinese). Also, some source codes are available from manufacturer. But, first of all, let's have a look at the hardware.

CH341A Mini Programmer Schematic

Heatsink for RTL-SDR dongle

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Some of the popular RTL2832U based DVB-T dongles that can be used as SDR tend to heat too much. As temperature increases, frequency drifts and sensitivity drops. Some dongles, especially those using R820T may stop working at all at high temperatures.

Marko Cebokli (S57UUU) used a thermal camera to measure the temperature of the dongle. He measured up to 85°C at the tuner chip (R820T). His images prove also that the dongle PCB doesn't do a good job at dissipating heat.

Although I'm using a R820T2 dongle (which is said to heat less than the predecessor R820T), I was surprised to see that after only 10-15 minutes the dongle was hot. Opening it up, I discovered that all ICs were hot (the tuner R820T2, the RTL2832U, the 1117 regulator, even the EEPROM was heated inside the closed case of the dongle).

Heatsink for RTL-SDR dongle

15-Segment FV865ND VFD controlled by HT16515

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FV865ND is a VFD panel manufactured by Futaba Corporation. It is designed to be used in DVD players or set-top-boxes. It can display 8 characters and it has a lot of symbols. I found it in a DVB-S2 receiver (Comag SL100HD) where it was controlled by HT16515 IC. Fortunately, the front panel of this receiver contains everything needed to power the VFD (the power is supplied via a 5V line and it is converted to filament and VFD voltage by a small transformer).

I couldn't find any software for HT16515 but its datasheet is available. The IC is 3.3V and 5V compatible and the nice thing is that the panel connector has different pins for IC supply and VFD transformer. The IC supports key scan too and the front panel makes use of only 7 keys (maximum 32). Data is sent/received via serial interface, SPI like.

15-Segment FV865ND VFD controlled by HT16515

SC75823 13-Segment LCD Display

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SC75823 is an LCD controller IC that is able to drive up to 156 segments. It is a 5V device that gets display data via serial bus. I found it in an auto CD player's front panel with 8 x 13 segment character LCD. I couldn't find an Arduino compatible library for it so I wrote one.

The controller only supports writing data to it. There is no key input support like other front panel ICs that can control a display and read pressed keys. The panel I'm using had each key connected in series with a different resistor and the main processor read pressed key by analog read value. Since some keys didn't work anymore, I cut the PCB and removed extra parts, keeping only the LCD panel, its backlight and the controller.

The communication protocol is probably Sanyo CCB (computer control bus), somewhat similar to SPI (it uses clock, data and chip enable signals). The controller has a pin INH that when LOW turns off the display. The library supports turning display off via this pin if connected or using software command.
Arduino SC75823 13-Segment LCD Display