Recent Posts

1

Projects, Designs, and Technical Stuff / Re: An interesting 3-transistor PSU from the old USSR "Radio" magazine

« Last post by Aramp on Today at 06:55:03 pm »

Well, I feel really stupid now.

The problem is that I have published the schematic that I started with, but then I introduced some changes as I did some experiments and, of course, didn't document them.
Of course, you are right that R4 can't be 3.3K. It is 680 Ohm.

By the way, you are right that the circuit does not start under the load.

2

Metrology / Re: Is anyone into quantum technologies and quantum metrology?

« Last post by RoGeorge on Today at 06:54:43 pm »

Something about quantum computers and quantum key distribution

Is that about using quantum encryption with classical computers, or does it includes hardware quantum computers, too?
 
I am curious about the hardware implementation of quantum computing in general, and about how are they built in practice (depending on which type of quantum phenomena they are based on).

3

General Technical Chat / any good way to emulate fast NOR SPI/QPI /etc FLASH with SRAM ?

« Last post by Hella_Wini22 on Today at 06:53:48 pm »

I'd like to play around with hardware that eitzher gets configured with ( FPGAs, FPGA SoCs etc) and/or execute code from such device (some microcontrollers, PC, CPUs etc).

To do this I'd like to use SRAM. Up to some extent, I could use onboard SRAM on FPGA, but those are quite small.

External DRAM is too slow latency-wise etc. Is there an obvious solution to this dilemma ? 🙄

4

RF, Microwave, Ham Radio / Re: Tuned Antennas Lighting Up LEDs Video

« Last post by Andy Chee on Today at 06:53:17 pm »

The diode is to allow reverse current to flow in the opposite direction.  If you remove the diode, the LED will block the reverse voltage, but will be destroyed because the reverse voltage became too high.

5

Projects, Designs, and Technical Stuff / Re: Bluetooth rotary phone from PTT T65

« Last post by pcprogrammer on Today at 06:52:33 pm »

About the schematic, it can do with some improvements to make it a mix between what Benta is stating and what you made. Connecting everything with wires might make it unreadable too, due to a mishmash of wires. For this busses can be used, but labels work too.

But that aside, the capacitors you used on the switches (dial is a switch too) might be a bit high. Maybe run some tests starting with 10nf up to 100nf. The switches might also work better with more current through the contacts, so also experiment with the pullup resistors.

Another thing, the bell driver, if you are using the original bell, it depends on how high VCC is, if it will ring. If I'm not mistaken, old phones used about 90V AC for ringing the bell. You can't have your VCC this high, and even half that will be to much for the TPS5430DDAR.

But a fun project none the less. Please post some pictures of the old phone and when finished the new insides.

Edit: Also look into what the microphone and speaker in the original form need to be driven. It might not work with the modern IC you choose.

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Projects, Designs, and Technical Stuff / Re: An interesting 3-transistor PSU from the old USSR "Radio" magazine

« Last post by Aramp on Today at 06:47:27 pm »

The voltage drop on VR1 is 1V when the load current is 0.4A.

OK, so since VR1 can't be more than 500Ω, this corresponds to at least 2mA current through VR1. This current should be coming from Q1 and from R4, so how is it possible if the output is set to 2.2V and there is less than 2V across R4?

There is something paranormal happening here

VR1 is 1K in my circuit (that's yet another thing I genuinely forgot to mention ). It is set roughly in the middle. And we have 1.6V across R4.

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Projects, Designs, and Technical Stuff / Re: An interesting 3-transistor PSU from the old USSR "Radio" magazine

« Last post by magic on Today at 06:45:50 pm »

Well, this shouldn't be possible. Are you sure that R4 is 3k3 and not lower and that RV1 is 500Ω and not higher?

If Q1:E is -1.6V and R4 is 3k3, then R4 current is 0.5mA and so is Q1 emitter current and so is Q1 collector current and 0.5mA should be not enough to produce 1V across RV1.

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Test Equipment / Re: Iwatsu SC-7205 Universal Counter

« Last post by coromonadalix on Today at 06:44:42 pm »

have you paid a lot for it ... pm me   loll

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Test Equipment / Re: Brymen 869s with BU86X does not connect under Win11

« Last post by coromonadalix on Today at 06:39:46 pm »

some talk there 

https://www.eevblog.com/forum/testgear/logging-data-using-brymen-bm867s-with-sigrok-on-windows-10-(bu-86x-usb-cable)/

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Projects, Designs, and Technical Stuff / Re: An interesting 3-transistor PSU from the old USSR "Radio" magazine

« Last post by Aramp on Today at 06:36:51 pm »

So, for easier reference. When the output current is 0.4A, and the voltage on input (after diodes) is 16.1V, then voltages on transistors are as follows:

Q1:E=1.6
     B=2.2
     C=15.1

Q2: E=15.8
      B=15.1
      C=2.8

Q3: E=2.14
      B=2.75
      C=15.75

If you want me to measure anything else, I'll be happy.