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Chaoyu CY-668A and ES-2008 Wireless FM TransmittersTechnical specifications do vary, probably due to misquotation than anything else, but they usually read something like this :-
| Parameter | 668A | Value | Notes |
|---|---|---|---|
| Operating range: | >5m | UP to 10M | Found to be considerably better in practice |
| Operating current: | 38mA | 45mA | See Power |
| Stand-by current: | - | 90μA | I measure around 1mA |
| Frequency response: | 20-20000Hz | 20-15000Hz | Commercial transmitters usually quote 30Hz min. |
| Stereo Separation: | >=50dB | 40dB | Typical quoted figure with commercial equipment |
| FM Deviation: | - | <0.01MHz | ±75kHz is appropriate for the band |
| Frequency stability range: | - | +10PPM | - |
| Distortion | <=3%(F=75kHz. f=1kHz) | - | - |
| Signal-to-Noise RATIO: | >45dB | >68dB | Meaningless figure |
Just below the display, to the right, you will find a row of 8 test points. I don't register any voltage or signal on the P7.x test points. I wonder if they are perhaps a bus to program the microprocessor.
| Marking | Function | Notes |
| GND | Ground | |
| P7.3 | ? | No voltage or waveform observed |
| P7.4 | ? | No voltage or waveform observed |
| P7.5 | ? | No voltage or waveform observed |
| P7.6 | ? | No voltage or waveform observed |
| P7.7 | ? | No voltage or waveform observed |
| RESET | Reset | Floats at 3.3v. Take this pad to ground to reset the device to factory settings |
| VDD | Power Rail | Off = 3.88v, Standby = 3.6v, TX = 3.25v |
There are three chips in this device, two on the rear of the board and one below the LCD display on the front. If yours is missing the stereo encoder chip then you possibly have the two chip variant.
| Chip | Marking | Package | Function |
|---|---|---|---|
| IC1 | None | Integral | Microcontroller |
| IC2 | GP214D 0633N | TSSOP 16 pin | Phase Locked Loop |
| IC3 | VL222 CP30B01 NJM2035 |
14 pin | Stereo encoder. It can be marked as any one of these three devices, and sometimes not marked at all. |
Being SMD, the components are a little tricky to identify. However, there are only a small number of semiconductor types and they appear to be as follows, although some may be any of the possibilities shown
| Marking | Dev. | Man. | Package | Type | Function | Characteristics | Datasheet |
|---|---|---|---|---|---|---|---|
| R25 | 2SC3356S | NEC | SOT23 | NPN | RF Final | RF fT 7GHz hfe 125-250 | |
| R25 | 2SC4226 | NEC | SOT323 | NPN | RF Final | RF fT 4.5 GHz hfe 125-250 | |
| J8 | BCX71JR | Philips | SOT23R | PNP | RF Driver | BCY79-ix |  |
| L6 | MMBC1623L6 | Mot | SOT23 | NPN | Torch switch | IC 100mA | |
| M6 | |||||||
| M1 | Voltage dropping diode | ||||||
| SS14 | High freq diode | ||||||
| 2101A 0616/33 | Chopper device for SMS | ||||||
There are three crystals on the back of the board. From top to bottom, these are
| Marking | Frequency | Notes |
|---|---|---|
| 38.000 | 38 kHz | For stereo encoder (19kHz x 2) |
| - | 32.768 kHz ? | Real time clock / microcontroller crystal? |
| SD10.2400 | 10.24MHz | Oscillates only when in transmit mode, presumed to be PLL reference OSC |
| Marking | Dev. | Man. | Package | Characteristics | Datasheet |
|---|---|---|---|---|---|
| R25 | 2SC3356S | NEC | SOT23 | npn RF fT 7GHz hfe 125-250 | |
| R25 | 2SC4226 | NEC | SOT323 | npn RF fT 4.5 GHz hfe 125-250 | |
| J8 | BCX71JR | Philips | SOT23R | BCY79-ix | |
As yet incomplete and in places erroneous schematic from what I've pieced together.
Requires Eagle by CadSoft
DOWNLOAD CY-668A SCHEMATIC
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