i already know how to work with already biased transistor but now i am struggling when it comes to designing one starting with these values, am using a voltage divider bias for the single stage. given these values, how do we go from there? voltage gain =100 VCC =18v and beta=120 and RL=1k also i need a way to find the emitter bypass capacitor and input and output coupling capacitor.
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I am trying to use a MCP3008 A/D converter (see https://ww1.microchip.com/downloads/en/DeviceDoc/21295d.pdf) with a RaspberryPi to digitize an audio signal generated by some legacy audio chip.
From what I understand I could just power the MCP3008 with 3v3 (VDD) to ease connection to the RaspberryPi (or I could use higer VDD up to 7V but then I'd have to use an additional levelshifter to interface with the Raspberry). The MCP3008's reference voltage for analog input signals cannot be higher than VDD+0.6V (e.g. 3.9V or 7.6V for the mentioned scenarios.).
According to the specs of the soundchip that I want to sample the relevant peak-to-peak voltage change is only 3V but the signal seems to ride at a 6V DC level. (I imagine that means that the signal moves within the 4.5V to 7.5V range.. is that assumption correct?)
I could obviously use some voltage divider to scale the input voltage to whatever maximum reference voltage the MCP3008 will tolerate. But I would always waste most of the measurement range 0 - 4.5V due to the fact that it is never used by the original audio signal.
Is there anything I can do to make sure that a respective A/D converter (it might be a different model than the one mentioned above) uses its measurement resolution to digitize
the signal specifically within the relevant voltage range? (i.e. with a 10-bit converter a 4.5V
signal should translate into 0 and a 7.5V signal into 0x3ff).
PS: I wonder if it might be a viable approach to use a Z-diode to cut off some part of the DC level and then measure the "overflow" portion of the voltage over a 10k resistor that I'd put after the Z-diode. Or are there any reasons why this might not work well for my application?
Use a high pass filter to remove the DC bias.
Given that you are working with audio you need to be careful not to remove audio data.
Im currently trying to get an electric signal from arduino, its 5v and 1amp that i get from a powersupply.
I want to input that signal into an arduino pin, lets say pin 4.
The main powersource from my arduino is via usb, but the 5v signal is from an external device.
I just want to know the number of time that signal became active, like a switch.
As far as i know arduino can take only .04amp from 5v.
Is there anyway i can reduce the current?
Anyway to obtain the value of a resistor to make it less dangerous for my arduino?
Your question is a very common application for Arduino!
You can give your Arduino some additional protection by placing a 10kOhm resistor between the Arduino analog pin you wish to use and the positive voltage output of the power supply.
If you're worried that the voltage could increase above 5V, you can protect your arduino with a simple voltage divider using two resistors. There's a detailed tutorial for this approach here: https://startingelectronics.org/articles/arduino/measuring-voltage-with-arduino/ Here's a simplified circuit diagram with a voltage divider that reduces voltage 11 fold - making voltages up to 55V safe to measure (where the battery could be replaced by your power supply):
For your code, you can use analogread() to read the voltage of the pin. If you wired it correctly, it should return near 0 when the powersupply is at 0, and 1026 or thereabouts if it is at 5v (or whatever the maximum value your voltage divider is designed for). Here is an example to get you started :
https://www.arduino.cc/reference/en/language/functions/analog-io/analogread/
If you need any support with your code to count the number of times the voltage goes high, post that as a separate question along with the code you have so far.
When I search online for EMG sensors, I often see these sensors are just made of a few transistors, resistors and sometimes diodes. Also I once read on a site that EMG sensors are some kind of modified voltmeters. But while I managed to make a voltmeter from an Arduino, I haven't been able to make an EMG sensor from an Arduino.
Does someone know whether it is possible to make an EMG sensor from an Arduino and how they did achieve this?
I think the biggest problem here is that of dynamic range. EMG signals are AC voltages typically in the low mV range and would need a gain of 100 or so to get them up to +/-2.5V, then a simple offset circuit to convert that to 0-5V for the Arduino analog inputs. However, that's not the whole story, since the small EMG signals can ride up and down on large low-frequency background voltages. Your AC amplifier would need a high-pass filter to remove those, or they could drive it off-scale which would prevent the EMG from getting through. If you reduce the gain to keep things in range, the EMG will be a rather small part of the 10-bit ADC range on the Arduino.
So the thing to ask is what is the point of using the Arduino in the first place? If you are going to connect it to a computer in order to look at the EMG signals, then why not just skip the Arduino and use the computer's sound card? The Mic input probably has enough gain already, and you get at least 16-bit resolution to handle any large non-EMG background that wasn't filtered out.
IMPORTANT! EMG measurements require direct electrical connection to the body. For safety, you should make certain that your recording equipment is electrically isolated. If you use only a standalone Arduino, you should power it from batteries. If you use a computer, it should be a laptop running on batteries, with no other connections to ground.
I often see these sensors are just made of a few transistors,
resistors and sometimes diodes.
That's true for pretty much all electronics devices...
Does someone know whether it is possible to make an EMG sensor from an
Arduino and how they did achieve this?
You cannot build an EMG sensor from an Arduino. But you read sensor values with an Arduino either through serial interfaces or by measuring voltages.
With a bare Arduino you can neither measure negative voltages nor can you amplify small signals. (we're in the µV range here...)
Just buy something ready or learn more on electronics
I'm planning to use the basic model of an arduino bike speedometer to count the amount of chain that I let out when I anchor my boat. However if I only have one sensor it would only work for the chain counting one way.
My theory is to have two sensors on the wheel so that if sensor A counts first then the chain is going out but if sensor B is counts first then the chain is coming in.
Only problem is I am much better at coding in python than I am in the arduino IDE. I would be super grateful if someone could give me an idea of how to do this?
From you application description, you really wan't to track the position of the wheel holding the chain, not the speed (or velocity). If you read how rotary encoders work, you can apply that technique to the wheel. Rotary encoders have two digital outputs which are out of phase by 90 degrees so you can not only detect motion, but direction.
See http://playground.arduino.cc/Main/RotaryEncoders for a detailed explanation
Would it not be more useful to count chain out and count back in?
Only 1 magnet on the chain gypsy that counts out your chain from the stowed position, picking up a 12v signal from the windlass direction solenoid lowering feed, stores this value at rest. When raising pick another 12v from the windlass solenoid raising feed to count the value back down to zero at the rest position?
This negates the need to determine direction by interpreting motor direction as count positive and count negative IO signals?
I am a CS guy getting started with Arduino. This is probably a very basic electronics question but from going over the arduino tutorials everything is connected to the arduino with a resistor.
Well since i am following the tutorials i know what type of resistor i should use but what i do not know is why i should use one? and What type of resistor to pick i am to do something which is not covered in a tutorial.
The resistor simply serves to limit the current into or out of a pin in case something goes awry. If your AVR decides to output high on a pin that something else wants low (or vice-versa), large, damaging currents can occur if not limited by some resistance. The current limit for AVRs is about 20 milliamps, and given that the voltages are usually 5V, something larger than 250 ohms "would work".
To give a margin of safety, 1-10k is a great choice; for digital signals it seldom matters unless you're into very high-speed applications (beyond the AVRs capability anyways). For analog inputs, a similar resistor would also be advisable, as the amount of current the ADC takes to sample is negligible when your resistor is in the few kilo-ohm range.
The underlying principle that you want to learn is Ohm's Law, which describes the relationship between voltage, resistance, and current in a circuit.
Resistors are used to
limit current,
devide voltage
protect against over voltage
pull-up, pull down
current to voltage conversion
etc ...
1) limit output current, the absolute max current per IO is 40mA, a typical LED works on ±2V 20mA.
the resistance value can by calculated by (5V - 2V)/(0.02A)=150Ω usually a 220Ω resistor is used, because: it consumes less power, there doesn't flow 20 milliamps, and there is no notable difference in emitted light.
2) if you have a analog voltage that variates between 0 and 10 Volts, you 'll need a voltage divider of 1/2. pick by example z2 10k and calculate z1 by 10k*(Vin,max/5V -1). take a value of resistance higher than the original calculated. and recalculate the new Vout.
3) place a resistor of 10k in series between the analog input of the arduino and the 'to measure voltage'
3) if you have to measure a analog current, you place a resistor to ground and the analog input, calculate the resistor by Z=5V/amps.
4) if you connect a button to the arduino, you 'll need to place a pull up or a pull down resistor. if you 're not using a resistor, the input is floating and can take any value (high or low). or you can enable the internal weak pull up. by pinMode(xx,INPUT); digitalWrite(xx,HIGH);. and disabeling by digitalWrite(xx,LOW); by default the pull-up is disabled.