One question being asked by members indirectly trying to answer a question in Q&A is, “How did you test the circuit?”
The answer you get from your meter or oscilloscope may not be what you get from your circuit there is a thing called LOADING EFFECT. Sometimes your meter lies to you.
This Instructable is about the proper testing of a circuit or prototype in order to answer the question asked so often in Q&A, “Why doesn’t my circuit work?”
Step 1: Overloading
However if you take this circuit outside in the sun all you get is a high pitch whine out of it unless you completely cover the photo resistors. The circuit doesn’t work the way it was designed because it is overloaded by light, the sun bounces off everything around you to your hand to the photo resistors.
This is called overloading and it is one kind of loading effect you need to avoid when testing a circuit or the circuit will not respond the way it is designed.
Step 2: Under Loading a Meter
In the first pic I connected a meter to a solar cell and got a voltage of 4.34 volts.
Next I connected an appropriate load in this case a 100Ω resistor to the solar cell as in pic two I play a lot with these solar cells from garden lights so I know what size of a resistor to simulate the circuit.
Then when I checked the voltage I get 3.34 volts as in pic three a one volt difference, making the first reading almost 25% out.
This loading effect is called under loading the current coming out of the solar cell is misinterpreted as voltage by the meter, unlike the complete circuit with the 100Ω resistor bypassing the current and showing the voltage.
If I wanted to make a 12 volt solar array with these solar cells I might use three solar cells if I were to use the reading 4.34 volts in the first pic and only get a 9 volt array when hooked to a circuit. However using the loaded circuit readout of 3.34 volts to make a 12 volt solar array I would use 4 of these solar cells and my circuit would work.
Step 3: Under Loading an Oscilloscope
This is the circuit from a Piezo buzzer that had the driver circuit in the buzzer. I accidently damaged the buzzer while disassembling the device it came from so I decided to reverse engineer the buzzer.
First I traced and mapped out the circuit with the values of the components I could tell with the help of my SMD code book. This didn’t work for all the components like the ceramic capacitors and the inductor coil since they had no markings.
Then I connected the circuit to my power supply and the output of the circuit to my oscilloscope without a load as in the next pic. Notice the distorted output signal and I am sure a 5 volt circuit without a step up transformer won’t produce a 63 volt peak to peak output. This is the loading effect of the current being confused by the oscilloscope as voltage.
Step 4: Everything Is a Resistor
In the first pic I replaced the Piezo Buzzer with a 10 kΩ resistor, this smoothed out the signal a little. If you know the load of the circuit you are testing you can just replace the component with a resistor and get the output you want, however that is only if you know the value of the component.
In the next pic I replaced the 10 KΩ resistor with a 50 KΩ pot and adjusted the pot until I got the strongest and clearest signal I could get then I disconnected the pot and checked the resistance.
The Piezo Buzzer’s specks are3 volts, 3 KHz, and 25 KΩ.
Armed with 3 volts, 3 KHz, and 25 KΩ I can find the nF for the Piezo Buzzer and then I can calculate the Inductor and capacitors using the formulas f = 1/2πCR, XL = 2πfL, and Xc = 1/2πfC.