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General Technical Chat / Re: Admit your Brain lock
« Last post by Sal Ammoniac on Today at 03:02:11 pm »
Why there's something rather than nothing.
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Overtemperature typicall is not that critical. If you want analog you can get an NTC and any comparator/opamp.
Like this: https://www.ti.com/tool/CIRCUIT060002
It is not accurate.

You can also use an LMT86, do the comparator/opamp but also feed the value to an ADC for readout, this is more accurate.

Make sure to add some hysteresis! Otherwise your board will powercycle.
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coastal areas and ports are sulfur emission controlled areas, so there they run bunker A which is basically diesel 

Sometimes they run cleaner fuel when in port and switch to the dirty stuff when at sea.

Even the lowest grade bunker fuel is lower in sulfur than it used to be. In fact, that change has contributed to global warming because higher sulfur emissions tended to mitigate warming.
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Microcontrollers / Re: PCB design question (crystal end ATmega)
« Last post by temperance on Today at 02:57:38 pm »
PCB3 is better than PCB4 because the stray capacitance to the plane is low in PCB4. But C5 en C8 could be placed a little further apart in order to decrease the capacitance in parallel with the XTAL.
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floating relative to mains

I assume you mean isolated as in going through a transformer?

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You can do the same with multiple power supplies too

This was a surprise as I would have assumed this would certainly cause ground loop issues.

Maybe I'm not understanding still, and apologize, but the visual still causes confusion. Let's assume my circuit needs 5 and 12V DC, for purposes of discussion 1A each, and a single ground (maybe 12V to power a display and 5V for logic). Now if my two-channel power supply has the grounds tied together, why can't the 1A that goes through the 12V circuit for the display see a lower resistance through way of the 5V ground and the full 1A from the 12V and full 1A from the 5V go through this channel thus sending 2A through channel 2 possibly blowing the transistor (let's assume the bench top supply can only supply 1A each channel).

In my head I'm visualizing the possibility of all the current flowing into a single channel whereas in a normal configuration, let's say two totally different circuits, the current is flowing in a loop within each of the bench top output channels.
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Test Equipment / Re: Rigol RSA3015N hacking or cheap options
« Last post by EE-digger on Today at 02:54:50 pm »
I think the lack of response sort of says where this topic is at.  The reason, I believe, is the super low prices on the Siglent products and their seemingly endless hackability.  From what I've seen with my hands on an RSA3030E I suggested a client buy last October, it's a well built product, not up to Agilent / Keysight standards, but very nice.  My concern on the N models is the very limited cal kit support.  Only 3 kits consisting of one of their kits, a second one with zeroes for all constants and a third, custom.  That's pretty poor as you'd have to store a STATE setup for your kit X, run a cal and save under "cal with kit X" for instance, same for Y and Z, etc.

How do you like your unit? 
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Thanks for your replies. These are very helpful to me.

A brief description of our application is that we have a MCU/FPGA board which is located a meter away from the application board. We are designing the PCB for the application board. The MCU/FPGA board is a kind of master board and it controls On/Off power supplies of the application board. There are linear regulators on the application board whose enable signal is controlled by the MCU/FPGA board. 

We need to measure the temperature on the application board and then implement the following two solutions for over temperature protection.

1- Measure the temperature with digital output for example using MAX31865 RTD to digital and send the digital measurement to the MCU/FPGA board. The MCU/FPGA will compare the temperature readings to a reference internally programmed. And if the measured temperature of the application board is above the certain value then it will cut off the power to the application board by disable the linear regulators.

2- The second option is to measure the application board temperature with analog output and then compare the measured output with a reference signal correspond to the shut down temperature. An OpAmp comparator on the application board which will disable/enable the linear regulators after comparing the measured temperature with the reference temperature. 

Please note that the temperature measuring circuits has independent power supplies on the application board.

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Beginners / Re: Mains Decoupling Capacitor
« Last post by Andy Chee on Today at 02:47:50 pm »
Not ESD.

More likely rudimentary EMI/RFI suppression.

https://recom-power.com/en/rec-n-class-x-and-class-y-safety-capacitors-142.html?0
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But why it picked up FM signals which lies in 101.1 Mhz? i have never seen something like that before... also the picked up signal was pretty clear...  i forgot to take a video of it happening :palm: also it only worked at that time
The op-amp doesn't need to oscillate at 101MHz to pick up an FM station.

What's happening is there's a tuned circuit somewhere, which is resonating at 101MHz. This is being rectified by a PN (diode) junction in your circuit and amplified by the op-amp.

It's an amplified crystal radio. Normally crystal radios are known for AM (Amplitude Modulation)  but they can work with FM (Frequency Modulation). In your case, the tuned circuit will have a sharp peak, so the amplitude of the resonance will change, as the frequency of the signal changes, resulting in amplitude modulation, which is being rectified.

Here's an article about FM crystal radio, if you're interested.
https://electronbunker.ca/eb/FMCrystalSet.html

Going back to your problem. It's probably lack of decoupling and poor layout. The low level signals should use screened, preferably twisted pairs. Also try adding ferrite beads to the outputs of the power supplies.

The schematic of your output stage also isn't clear to me. Please use proper symbols, rather than just boxes.

yeah i also figured it out. it was the power amplifier not the opamp. I was actually making a 30 watt class ab amplifier that could run on single supply. but the problem is my phone cannot run it. needs a pre amp. single transistor preamps don't work with this poweramp. actually the power amp circuit is coppied from a random youtube video. also it was the only circuit that could be any loud otherthan the overheating ones. also the video claimed it could give out 50 watts which i dont think so.. on testing it that circuit could only give out 5 watts...
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kreyren on 29 March 20, 2024
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DiTBho on March 20, 2024
Just checked, the pinetab2 uses the Rockchip RK3566 SoC

Afaik the reason why OLIMEX didn't provide the RK3399 and RK3566 is that they were very unreliable software-wise (afaik they release the chip and then rely on the community to mainline them while not providing sufficient amount of documentation?) and tsvetan not wanting to support that as the resulting mainline is often very problematic and takes long time to get implemented in a way that is acceptable in industrial settings (OLIMEX's main focus)

For me in terms of arm architecture only use Cortex A7/53/55 and consider everything else garbage due to the CPU vulnerabilities, but i plan on supporting all chips as long as the required docs to make boards for these are available or unless someone wants to do the adventure of reverse-engineering them and contributing that (that's what the SOM management is meant to be for)

This is one of the public responses, which explain the reasons for the choices made.
I'm a bit perplexed, because it seems like it's always the same problem regarding software development, documentation, etc  :-//
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