New answers tagged ttl
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A floating TTL input can be considered 1.
Then again, one cannot rely on this. Neither switching speed nor the noise immunity will be the same.
Leaving a TTL input to pull itself is good only for "try and see" and nothing more.
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Adding to swineone's answer, I prefer to use the dfu-util command line tool (more info) with a batch script. I simply hold the boot button while plugging in the board, or better yet have a second reset button to quickly power cycle the board.
Then, I double click my batch script and it automatically flashes the board and returns it to normal operation.
set ...
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Many (if not most?) RS232 receivers actually will accept unipolar signals not reaching officially valid logic levels.
However RS232 line drivers and receivers have by tradition essentially always been inverting, so if you want to use this trick with an MCU or whatever following usual conventions, you need an inverter. (A very few UARTs have a mode bit which ...
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An old fashioned TTL high is not +5V, it could be only +2.4V and still be valid.
A TTL low can be +0.4V.
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Simulate this and you will get 2mA in both the LED.
replace SW1 with your GPIO directly.
simulate this circuit – Schematic created using CircuitLab
All resistor value hard to find so use, R1 = 3.7KΩ & R2 = 1.1KΩ
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Figure 1. Image source: 1 GPIO, bi-colour, 2-pin LED.
Try converting the parallel resistors into an equivalent voltage source.
simulate this circuit – Schematic created using CircuitLab
Figure 2. When R1 = R2 then the equivalent source voltage is V/2 in series with R/2 (R1 and R2 in parallel).
If we take Vf = 2 V as an average for the red and green we ...
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The easiest solution would be either use a single optocoupler per signal, or optionally a optocoupler with multiple devices in a single package (e.g. DIP-16 with 4 optos)
Here you can see a schematic how it could be done:
Image source: Amazon - Icstation 24V to 5V 8 Channel Optocoupler Isolation Board
Optionally a Schmitt trigger can be used on the 5 V.
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Yes, using an Arduino Sketch - see “Poor-man’s boot loader upload” in:
https://git.jeelabs.org/jcw/embello/src/branch/master/projects/ask/stm32f1init/stm32f1init.ino
See more on https://jeelabs.org/book/1546c/index.html
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