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OPPO Find X8 Ultra's dual-tone camera module revealed
A tipster has just revealed the OPPO Find X8 Ultra’s dual-tone camera module ... you’ll see an LED flash, outside the camera module itself. Then, the top module in the camera module is ...
Hackaday7y
In-Band Signaling: Dual-Tone Multifrequency Dialing
One late night many decades ago, I chanced upon a technical description of the Touch-Tone system ... channels to generate the dual tones, I bet I can dial the phone! I sprang out of bed and ...