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2 votes
Accepted

Reducing EMI caused by unterminated serial TX line

When something is connected, the receiver will be a high-impedance CMOS input, which behaves pretty much the same as an open end. So there is no practical difference between connected and unconnected. ...
CL.'s user avatar
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0 votes

Why does my opto behave like this?

A phototransistor can be roughly modeled as a transistor with a light-to-current converter and capacitor between the base and the emitter. When the LED is turned on, the capacitor will be charged up ...
supercat's user avatar
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2 votes

Why does my opto behave like this?

Claiming speed for these kinds of optos with a 100Ω load (large print) means you have to read the fine print to find out what the speed is with a much higher load resistor (the way folks normally use ...
Spehro Pefhany's user avatar
1 vote
Accepted

Some characters lost in UART Transmission (PIC12F1822 -> SIM800L)

Most likely there is a race condition between the code you have listed and the IIC code that you did not list. I assume the IIC code updates UARTTXBuffInPos from an ISR when IIC data is received. If ...
Steve Mathwig's user avatar
5 votes

Why does my opto behave like this?

From LITEON data sheet: Although this test is for Idiode=5mA, you get the idea of its speed. To get a current-transfer-ratio near 1:1, transistor current gain (HFE) is likely quite high, which slows ...
glen_geek's user avatar
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7 votes

Why does my opto behave like this?

Why does my opto behave like this? Look at the rise time graph for a 1 kΩ load: - I'm sure you can find an opto-coupler that is a lot faster than this and, one that has a digital push-pull output. ...
Andy aka's user avatar
  • 453k
11 votes

Why does my opto behave like this?

The LTV-817 is a "general purpose phototransistor photocoupler". It is not rated for such fast data communications. So it is behaving as expected. The transistor is on for quite a long time ...
Justme's user avatar
  • 144k
0 votes

Why does my opto behave like this?

Seems this optocoupler is naturally slow with 4us rise and 3us fall times. So it is not sufficient for high speed switching.
Michal Podmanický's user avatar
2 votes

Why does my opto behave like this?

The response time could be as high as 18us (see page 10 of the datasheet). Also, what is the drive current of the GPIO of the MCU? You are likely current-limited. Try driving the LED with more juice. ...
MOSFET's user avatar
  • 2,095
0 votes

STM32 USART RX with DMA

Couple of pointers: There's no need for this callback as it's not needed void USART3_IRQHandler(void) You've set only 20 bytes to be transferred. So it'll stop after 20 bytes. When it comes to DMA ...
EmbeddedAlpha's user avatar
1 vote

Some characters lost in UART Transmission (PIC12F1822 -> SIM800L)

Internal oscillators are not precise enough for UART communication. Adjust the oscillator frequency or baud rate up or down to try narrow down when it works, or use autobaud detect feature of the MCU....
Justme's user avatar
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0 votes
Accepted

ESP32-CAM flash via UART

The TXD pin on Arduino is MCU TXD out to RXD of PC. You need to connect the TXD output of ESP32 to TXD pin of Arduino in order for the PC to receive data. So connect TXD to TXD and RXD to RXD. The UNO ...
Justme's user avatar
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2 votes

Do I need a pull up or pull down for the optoisolator in a USART application?

No difference to signal quality. The isolation capacitance is far smaller than the phototransistor output capacitance (or the internal B-E junction that actually receives photocurrent), and common-...
Tim Williams's user avatar
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0 votes

Do I need a pull up or pull down for the optoisolator in a USART application?

For signal integrity or slew rate, it makes no difference whatsoever. So you can choose based on the polarity of your signals. The typical UART connection is case 1 because it saves power when idle, ...
CL.'s user avatar
  • 19.2k
1 vote

How to identify protocol of unknown 7 segment display chip?

There are a number of display driver chips which require only clock and data lines. For example, the GN1640 by GN Semiconductor, also made by Titan Semiconductor as the TM1640. Your traces look like ...
Spehro Pefhany's user avatar
0 votes

Why does a PB-02 ignore a "AT+NAME=abc123"?

I found this PDF via Google. It says that it is "BLENAME" in v1.1.3. ...
RRIDDICC's user avatar
1 vote
Accepted

STM32 UART in LIN mode sends with incorrect baudrate but not in asynchronous mode

The stop bits must be set to 1 in LIN mode. That and other prerequisites for proper operation in LIN mode is specified in the reference manual for the MCU. Basically, if you are not using other weird ...
Justme's user avatar
  • 144k
0 votes
Accepted

Why would a UART only transmit the first character and then stop?

Most likely the code is fine, and the problems are receiving the data in hardware or software. You are using a 5V Arduino with Atmega16U2 as the USB to serial adapter for a (likely) 3.3V signal. It ...
Justme's user avatar
  • 144k
0 votes

Do not get how to time PIC16F USART sending in interrupt-driven environment

OK, you are using RS-485 so you anyway have a half-duplex medium and generally you can't receive on RXD what you send on TXD, and, you must reserve some turnaround time, during which, the byte ...
Justme's user avatar
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