Hello,
I have been trying for a few hours to make this very simple circuit work with an Arduino but I have FAILED miserably
I have a BC547 Transistor and an Arduino UNO
Currently the circuit is this.
Anyone touching the Antenna then the LED gets brighter. So a really simple circuit..
So how can I put an Arduino UNO in to replace the LED and capture the voltage/Signal
Can someone point me in the right direction.
Thank you
Replace LED with resistor, measure collector voltage?
Also perhaps add a capacitor in parallel to the resistor to smooth fluctuations.
I'd suggest 100k as an initial trial value for the resistor - if the voltage ends up too low (1V or less),
halve the resistor value until the voltage isn't quite so low.
Thanks for that, though I think I have just trashed one of my UNO trying the above, I suspect I put a lead in the wrong place, so can I ask how I would measure the collector voltage.
I used the code below and the layout
int CollectorPin = 5;
int CollectorValue;
void setup() {
// put your setup code here, to run once:
pinMode(CollectorPin, INPUT);
}
void loop() {
CollectorValue = analogRead(CollectorPin);
Serial.println(CollectorValue);
}
But nothing happens on the UNO. ie all the onboard LED do not light up. Should plus the A5 lead elasewhere??
all the onboard LED do not light up
Then I would suggest something is shorting out the power supply. If you wire it like you said then this won't happen.
So post a schematic and a photograph of the wiring.
int CollectorPin = 5; // Digital 5 or analog 5?
int CollectorValue;
void setup() {
// put your setup code here, to run once:
pinMode(CollectorPin, INPUT); // digital 5
}
void loop() {
CollectorValue = analogRead(CollectorPin); // no, analog 5!
Serial.println(CollectorValue);
}
If you are using a pin number in both a digital and analog context, use A5, not 5.
However you don't need to call pinMode, INPUT is the default. This code will work
if you remember to call Serial.begin in setup() with a baudrate that matches the
serial monitor setting.
SniffTheGlove:
Hello,I have been trying for a few hours to make this very simple circuit work with an Arduino but I have FAILED miserably
I have a BC547 Transistor and an Arduino UNO
Currently the circuit is this.
- -LED- Collector
Base -Resistor-Antenna
GND EmitterAnyone touching the Antenna then the LED gets brighter. So a really simple circuit..
So how can I put an Arduino UNO in to replace the LED and capture the voltage/Signal
Can someone point me in the right direction.
Thank you
Sounds like a wet finger test of an NPN transistor.
Grumpy_Mike:
So post a schematic and a photograph of the wiring.
Post your diagram.
Apologies for earlier posts, now removed.
Please see
As you can see a simple circuit.
Red lead goes to Arduino 5v
White lead goes to Arduino GND
Orange lead goes to probe/antenna
If I plug the a lead that goes from Arduino A5 into the breadboard with the resistor & 5v red lead is I get 1023 as my reading on A5 all the time, which is what I kind of expected.
If I plug the a lead that goes from Arduino A5 into the breadboard on the other side of the resistor I still get 1023 as my reading on A5 all the time, which is NOT what I expected.
Where would I put the my lead to measure the collector voltage
I am trying to accomplish the same thing as http://www.instructables.com/id/Ten-Breadboard-Projects-For-Beginners/step9/Project-3-Static-Electricity-Detector/
But use a Arduino to measure and store the value to SD card. For simplistic effect I am just using a single transistor first to understand how it works.
It is hard to say from your picture - is the resistor from (red) 5V connected to base or collector?
When you connect the A5 to some other known voltage do you get expected reading from Arduino?
Is the transistor working - are you able to turn on and off a LED with it with known current?
Can you check all voltages with DMM to see if they are as expected?
The circuit you linked to will be either saturated (on) or off.
If you are wanting to get a useful measurement of pickup from an antenna you will need a different circuit.
SniffTheGlove:
as my reading on A5 all the time, which is NOT what I expected.
It is exactly what i would expect.
The first transistor requires current not voltage to turn on pickup from an antenna will be insufficient to turn it on.The whole circuit only works due to its configuration giving very high gain.
Try connectin the antenna to +5 V with a 10 K ohm resistor repeat your measurements.
Try it with other values and see what changes.
Nothing less than 5 K though and you should be safe with that transistor.
Where would I put the my lead to measure the collector voltage
Put it to the collector of the transistor, the one where nothing is connected in that picture.
Now hold the lead in one hand and with the other hand lick a finger and put it to the 5V line. Do you see any change in the reading?
I am trying to accomplish the same thing as.....
Instructables are in general crap, written by people who don't know what they are doing, read by people who have even less idea. However, why are you only using one transistor while that circuit is using three? The three are cascaded so that means the gain of each transistor is multiplied together.
The BC574 has a gain of about 90, you that is what your circuit has.
The one in in the Instructable diagram has a gain of:-
90 * 90 * 90 = 729,000 times
Is this any clue as to why you are not seeing anything?
Can you post your schematic please. A schematic has things like resistor values on it.
Thanks all,
Grumpy_Mike first. The reason for a single transistor was to make it simple at first so I can try and understand everything.
Originally I had the circuit which had an LED in it. Thus touching an antenna the LED would make the LED brighter.
Then I wanted a way to record it onto an Arduino connected Network Shield SD card for review on a PC
So using a single Transistor would be my starting point and then add the extra transistors sequentially to boost the gain until I would saturate the Arduino signal.
Smajdalf now. The resistor 82ohms on the 5v is attached to the collector.
The resistor on the Base is 10k which then goes to the antenna.
Emitter is to ground.
Here is a Fritzing
Try to use larger resistor for the collector - I have no idea how large signal you can get from the antenna but I am quite sure it won't provide much current. I would try 100k at first try?
So using a single Transistor would be my starting point and then add the extra transistors sequentially to boost the gain until I would saturate the Arduino signal.
So when this did not work at all why did you not go for the two and three transistor versions? No idea what saturate the Arduino means, it is something you can't do.
With a bigger signal picked up the voltage you measure will go down, at the moment it is not even beginning to move.
Yes 82R is way too low. To get a voltage drop of 1V then you have to have 12mA flowing down it, and with a gain of 90 you would have to have a current of 135uA in the base. This is way way higher than you are going to pick up with an antenna. Use a 1M resistor but I am still not sure if you will see any voltage movement with this and only one transistor.
Can i ask if you have any potentiometers in your kit and if so what value. ?
Also the link you provided shows a circuit diagram with values , did you understand it ?
Do not use fritzing diagrams if so , they suck.
Draw on paper and post a picture showing component values.
Your trying to build an electroscope - that cannot be done using a bipolar transistor due to the minimum base bias voltage (~0.6v). Electroscopes are build using JFETS such as the J310. Plenty of designs online. Just search for FET electroscope or FET electrometer
The meter in the electroscope design can then be replaced with a fixed resitor and the voltage across it beasured using one of your Analog input pins.
I doubt such thing cannot be done with BJT. Where is difference between base bias voltage of BJT and cutoff GS voltage of FETs?
Smajdalf:
I doubt such thing cannot be done with BJT. Where is difference between base bias voltage of BJT and cutoff GS voltage of FETs?
Try it....
G7MRV:
Try it....
I do apologise! That was very flippant of me!
I believe it is not so much the difference in biasing, as the difference in input impedance.
Although a static charge can be many tens of thousands of volts, the available current on discharging that field is negligible. When that charge has to flow through a very low impedance, the resulting current demand would cause the voltage to collapse to negligible, and so fall below the bias voltage required. Hence a BJT wouldnt work. That said, if you really charged yourself up you could probably 'just' trigger one!
A JFET has a much, much higher input impedance, and so the required current flow from G-S is tiny, and although it does discharge the field, its enough to allow the JFET to operate and provide an output. Ive built several JFET based electroscopes, and there is no additional biasing needed.
I would say though that a BJT based amplifier would probably make sense after the JFET detector, this would buffer the JFET and prevent the Arduino input from loading it. The resulting voltage swing at the output of a simple BJT emitter follower would make reading it by the arduinos A-D converters easier.
