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Help identify glass encapsulated diodes

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fzabkar:
U18 consists of 3 SPDT analogue switches. Pin #10 is a control input. A high or low on this pin connects pin #15 to either of pin #1 or pin #2.

https://www.mouser.com/datasheet/2/916/74HC_HCT4053-1541743.pdf

晓看风云:

--- Quote from: fzabkar on August 26, 2024, 07:46:55 pm ---U18 consists of 3 SPDT analogue switches. Pin #10 is a control input. A high or low on this pin connects pin #15 to either of pin #1 or pin #2.

https://www.mouser.com/datasheet/2/916/74HC_HCT4053-1541743.pdf

--- End quote ---
I understand this, but what I don't understand is that the set frequency is generated by the MCU. Why did it end up here instead of going to the output terminal? If I set the frequency to 100Hz, then this 10 pin will display 100Hz very stably. I am very puzzled about this... and assuming XL is a field effect transistor model 2sk209 bl, what is the purpose of directly short circuiting the source and drain of pin 1 and pin 2?

Kim Christensen:
Perhaps they are using it as some sort of crude, or ingenious, DAC.

Just a guess and probably not how it's designed:
If you wanted to generate a square-wave that swung between 1V and 3.5V you could feed these two DC voltages into pins 1 & 2, and get a square-wave out on pin 15 that toggles between 1V and 3.5V at the same frequency as the logic level signal on pin 10.
If the 1V and 4.5V were missing (at zero V) then that would explain why the "signal" at pin 10 seems to go nowhere. Or, if pin 6 (INHibit) is at logic high, then all analog switches would be disabled with the same result.

fzabkar:
U15 and U16 (?) appear to be 4053BF ICs. U18 looks different. :-?

https://docs.rs-online.com/8004/0900766b8082f4fe.pdf (Toshiba TC4053BP / BF / BFT)

晓看风云:

--- Quote from: Kim Christensen on August 26, 2024, 08:18:06 pm ---Perhaps they are using it as some sort of crude, or ingenious, DAC.

Just a guess and probably not how it's designed:
If you wanted to generate a square-wave that swung between 1V and 3.5V you could feed these two DC voltages into pins 1 & 2, and get a square-wave out on pin 15 that toggles between 1V and 3.5V at the same frequency as the logic level signal on pin 10.
If the 1V and 4.5V were missing (at zero V) then that would explain why the "signal" at pin 10 seems to go nowhere. Or, if pin 6 (INHibit) is at logic high, then all analog switches would be disabled with the same result.

--- End quote ---
I have been thinking about whether pin10 can output the correct frequency from pin15, because this signal has no way out unless it encounters an unfortunate disconnection. After listening to your answer, I realized that pin1 and pin2 still need to cooperate, so I will follow them. Don't worry, pin6 is always in a low level state. I vaguely remember testing pin1 and pin2 with a multimeter before, and they both had no voltage, only a weak mv. Also, I just discovered an interesting phenomenon. If I touch both pin1 and pin2 of the LT1012 operational amplifier at the same time, the output port will display the frequency value I set correctly! And both LT1012 can

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