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

« Last post by Zipdox on Today at 08:40:41 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.

I'll take it into consideration.

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.

I plan to do some debouncing tests with the switches before I finalize the design.

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.

The bell already works with 10V. I tested it with a DRV8833 I had on hand at 12V and it's plenty loud. VCC will be 12V.

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.

I also already tested the microphone. It's a carbon microphone. I tested it with a 1k resistor and 3V bias supply. The output signal is pretty strong, so I'm pretty confident that it'll work. As for the speaker, it's 100 ohms, so I might need to look into that. Maybe using the speaker output instead of the mono output is a good idea.

I don't know what you're planning to use for the software component but I successfully wrangled Espressif's bluetooth stack to provide telephony services in my weeBell project.  I did things a bit differently than you are planning to but just in case you'd like someone else's code to look at: https://github.com/danjulio/weeBell_bluetooth

The hardware my code ran on is at: https://github.com/danjulio/weeBell_hardware

I had to deal with echo cancellation which you shouldn't have to as you're interfacing separately to the handset speaker and microphone.

Thank you for the link, I'll definitely look into that. I already did some research regarding Bluetooth capabilities, and saw that many ESP32 variants don't support Bluetooth classic, only Bluetooth LE. So I successfully avoided a possible disaster of HSP/HFP not being possible. As a side note, have you considered using a hybrid transformer instead of echo cancellation in your device?

I second pcprogrammer's comment:  Make sure your DC input can ring the bell if you haven't already (they will ring, less loudly, on lower voltages).  Also make sure the levels into and out of your codec are ok.  The codec looks like it wants to drive a 8-16 ohm load.  Your old phone speaker might be higher impedance.  Fortunately the codec has an amp on the input for the microphone.  You might have to adjust that some however.

Yeah I'll look into the datasheet. I might end up using the speaker output rather than the mono output.

I think you should include a 1uF cap between EN and ground.  Espressif recommends (IIRC) a 22 uF + 0.1 uF bypass cap on the input which you more-or-less have with two distributed 10 uF caps on 3V3.  If you're running I2C at 400 kHz then I'd lower the values of the I2C pullups to something like 2.2 kohm.

The reset button and pullup resistor will be right next to the enable pin of the ESP32 module on the PCB, are you sure that's necessary. Espressif doesn't mention this practice in the datasheet either. As for the I²C pullups, I think I'll use 3.3k so I don't add another BOM entry. The line won't be long anyway.

Also, I'd recommend to include the ubiquitous 2-transistor auto-programming circuit using DTR# and RTS# from your USB UART (bring them out on H2) so you won't always have to be doing the BOOT/RESET button dance when you load code.

I don't even know if I have a USB-UART adapter that has those pins. I've been pressing boot and reset on my dev boards for ages anyway, and I'd like to save on board space and number of different components.

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Test Equipment / Re: LCR Tweezer Fnirsi ST1 vs. Zoyi MD1

« Last post by DaneLaw on Today at 08:39:15 pm »

..
When it is in off state, you need to push the toggle knob at left and push power button  at same time to go in such mode.
Then you see the calibrate screen and you can select calibrate value between short, 1, 10, 100, 1k, 10k, 100k, 1M,10M and open.
..

Thx for the info, and yes there is a hidden cal-menu that pops out with toggle-to-left (while a push-in activates bootloader)
Do you know if such a manual calibration takes precedence over the different ways to reset it, or will "restore" flip ST1 back to scratch?.

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

« Last post by hulk69 on Today at 08:36:55 pm »

looking at it again makes no sense because the diodes are reversed...

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Beginners / Re: How do I find the matching solder points?

« Last post by MathWizard on Today at 08:36:38 pm »

Looking at that PCB, is there a clear coat/conformal coat on there, to keep out the moisture ? That might throw people off when trying to measure on the PCB. Some solder also get a pretty thick oxide layer, and you really have to stab into the solder, just to get a decent reading.

I tried cleaning some coating off an dishwasher PCB, with ISP alcohol, it didn't work that good. So soldering into it the whole time.

Even with rosin solder, having some flux to add to the solder joints, makes things way easier, just make sure to clean it good afterwords, some fluxes have to be cleaned, they can be full of conductive sludge.

I didn't have flux for a few of the early DIY PCB kits I soldered up, and the solder never took to most of the via's. or pads. I'm sure I would have over heated them in my attempts too, so it wasn't that.

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Projects, Designs, and Technical Stuff / Re: Relatively high voltage precision DAC amplification

« Last post by Zero999 on Today at 08:32:47 pm »

Any suggestions for main transistor Q1? Seems like a candidate for some series (cascode) devices.

The base drive for Q1 might be an issue - trade off between power dissipation and required amplifier headroom.  It would seem that a constant current source would do better, but I’ve never built such a high voltage linear circuit; maybe someone who has experience with such designs could comment. There’s nothing intrinsically wrong with just using a resistor and a higher DC input bus.

Some other features come to mind…
- output enable/disable feature
- overcurrent protection
- constant current pulldown so output capacitance can be discharged a bit faster than the divider resistance alone

A cascode is a good idea.

Here's an idea which uses an NPN cascode to drive a PNP cascode. Each transistor only ever sees up to a third of the supply voltage. I recommend more than just three transistors in each string, perhaps eight or ten, that way ordinary jellybean parts can be used.

Note that the safe operating area of BJTs means that to get any more than a couple of mA, more than one device, whether it be in series (cascode) or parallel (use current sharing resistors), is required. In this case since it's high voltage, not current, cascode makes more sense.

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FPGA / Re: SD card/SDIO 3.0 level translation solution

« Last post by asmi on Today at 08:31:29 pm »

No, only cards supporting full LVS (Lv? seems to be just confusing?) but from my understanding all A2 application class cards must support it. My Samsung EVO Plus A1 card also does so.

All microSD cards are required to support commanding to switch to 1.8 V signaling. Are you saying that all microSD cards support your way to start them in 1.8 V signaling?

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Test Equipment / Re: Test Equipment Anonymous (TEA) group therapy thread

« Last post by khs on Today at 08:30:09 pm »

Scope works perfectly but whenever it decides to start misbehaving, it will be the end for him... this beast is so complicated (with no proper service manual to boot) that I just wouldn't be able to fix it.

Here you can find the service manuals for the TEK 11401:
https://w140.com/tekwiki/wiki/11401

After auto-calibration the 11K oscilloscopes are quite accurate (about 1%) and have a quite short overdrive recovery time of 50 ns from a 2V step at 1 mV/div for the 11A32.

So it looks to be worth to keep the monster running..

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

« Last post by hulk69 on Today at 08:29:57 pm »

After thinking a lot about this i do not think it has anything to do with protection because of the very minimal power involved but more about the voltage/current characteristic of a fast diode.

An LED would need a lot more current to get to a certain voltage.
The schottky diode can start conducting @100µA -> 0.4V which would be able to drive an LED very dimly

So my theory is that the diode is there to increase the voltage at very low current

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Test Equipment / Re: SDS800X HD Bug Reports + Firmware

« Last post by Furna on Today at 08:29:48 pm »

As for the rest, can we quit the bitching and hyperbole and be specific and deterministic on this. No one is going to listen to you if you suffix everything with generic complaining.

I would suggest to stop answering; this person is not going to listen.
I suggested to keep discussions/complains in different/dedicated thread and bugs and feature requests in dedicated threads; the result is more noise on those threads as well.
Also other threads were started ... I guess the objective is just trolling.
I do not see other action we can take other that simply ignore.

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FPGA / Re: SD card/SDIO 3.0 level translation solution

« Last post by KreAture on Today at 08:29:32 pm »

That's exactly what they have done. My code proved that it also works!
All that is needed is a single clock pulse of a long duration and card will acknowledge the switch before any commands are sent. All you need is to pull the pins low instead of high to start with, and give this 1.8v clock pulse. Card will respond with pulling DAT2 high (1.8v levels high). Once you start feeding it clock pulses the card will release the high drive on DAT2 after about 2 pulses and a slight delay.
As long as you want to communicate with card over SD protocol it is now ready for the normal init. Just remember that SPI can now not be enabled unless you power cycle card.

Is this compatible with every single card out on a market?

No, only cards supporting full LVS (Lv? seems to be just confusing?) but from my understanding all A2 application class cards must support it. My Samsung EVO Plus A1 card also does so.