The ideia is to do not consume so much current from the source. For example, if you're using an 5V microcontroller, given an 1k resistor, each pin would consume 5 mA when in HIGH state. Now imagine 10 or 20 pins at same time, your micro would be driving 50 - 100 mA.
In many cases it's a 10k resistor.
I dont know how much current an LED needs. When meausured, a blue LED with around 2.8 volts on it draws about 7 miliamps
The thing about LEDs is that you decide how much they draw. You can use a resistor or a constant current source but ultimately you should (and need to) decide how much current will go through them.
You can power LEDs directly from the ...
If you want amplifiers, take Instrumentation OPamp such AD622.
Sample/hold components (LF398) would be helpfull, but not really needed.
You can then use a microcontroller who ADC speed is fast enough. I think a STM32F1.. (BluePill) is ok. Raspberry too. Some 16/24bits ADC boards can also be used if they are correctly interfaced.
Example : AD7606 (16 €) ; 16 ...
Pins 21 and 22 are the i2c pins. So I’d say that is a QWIIC connector or whatever the other suppliers call it. You can purchase various boards from Sparkfun et al that plug into that. I have a little oled module using that interface.
The IRF520 is not the best choice. In your application it is borderline as to whether it will work. This might go some way to explaining your problems.
I'd suggest you choose a mosfet that is 'logic level'. Something like a IRL3705Z. The 'Z' is significant.
330R is a strange value, 10 or 22 ohm is more sensible. This resistor is called a 'gate stopper' to ...
You're lucky: body impedance measurements are a simpler problem than measuring external voltages in presence of noise. As long as you can keep the electrode-to-skin resistance relatively constant by strain-relieving the leads so they don't tug on the electrodes, it's not hard to get good signals.
The core idea is to drive a small AC current through the body,...
When you're searching for a DC-DC converter, there are a few questions to ask first:
What are your maximum and minimum input voltages? (In this case, presumably 4.2V and ~3V, from a LiPo battery.)
What is your output voltage? Is it lower than your minimum input voltage? (Buck converter) Is it higher than your maximum input voltage? (Boost converter) Is ...
Coin cells have a high series resistance like 1k+ depending on size, so read specs to estimate voltage drop.
The gecko M0 CPU’s operate at about “ 114 μA/MHz” so 32kHz would be low current but 24MHz would kill the battery.
Therefore consider a much larger battery.
If either ECHO or TRIG is low, the sensor will probably be grounded through protection diodes. You could use high-side switching (on VCC instead of GND) but the same applies...you can get voltage from any input through your high-side protection.
Best bet is to use your same circuit as above, but make sure the other inputs are set to 5V when you're power ...