Function generator power up and testing after assembling

Here is the video covering all bellow details in video:

Any electronics kit when assembled, before powering it up one must check it very thoroughly. There should be no mistake, no missing, no omission and no self made defects like soldering bridges, dry solder joints, reverse components etc. The circuit developer should put a very careful eye on everything he or she populated on the board. This instruction is more critical and hard for pref board and veroboard circuits. As they are not critically designed and review so more care is needed in such a case. The personnel should take extreme care and observation as a small mistake can lead to no function board or lead to further damage in some cases. 

When powered up a board for the first time, the voltage should be checked at certain points. Those points can be provided by board designer or by the developer him self. So when the voltages at certain points are correct and not beyond the possible limits, the the board should be checked for signal production and output of the board should be monitored when certain input is applied and other parameters are set to preset values. The circuit should work as expected.

Mostly when new developers develop their circuits, they refuse to work at first power up. The problem is as express in the above lines, lie somewhere. Sometimes the entire schematic diagram is wrong and misleading. This was happening in older days of late 1900. Now as internet is everywhere so people are getting benefit of it and they search for any circuit according to their needs and they get the specific and working design very easily and no one can mislead them.

Multimeter is a useful tool to test for voltage and resistance. But that is very useful to test DC voltage levels are different points. Whereas oscilloscope is very useful to test for waveform and AC voltage levels of high and mid range frequencies. To power up a circuit or to design a circuit one must have multimeter as well as a good or average oscilloscope. Without these two tools it is very difficult to develop an electronic circuit. Good tools are always paying themselves. Acquiring good tools should be essential for a person dealing with electrical and electronics. 

The function generator we developed here has four functions. There are sin wave, triangular wave, saw tooth wave and square wave functions in this generator. The testing should be started for DC power where the power is entered in the board. I checked 8.999V DC at power adapter output as it was 9V DC adapter.

The circuit input voltage is being tested.

Then measure DC voltage at different points like IC pins and transistors. Look at the schematic diagram for voltage reference and the specific pin numbers containing those voltage levels. If level is good at the certain pints, proceed further. In my case there was pin 1 grounded and on 4 and 8 there was supply voltage and there was a diode in series with the supply voltage. So it was 8.29V. i.e. the diode forward bias voltage drop was 0.7V.

The voltage is being tested on the 555 chip pins.

Then as all voltages were good measured, we further proceeded to the circuit output and tested DC voltage at out put of the circuit.

The output of the circuit is observed using DC range on multimeter.

We got Zero volt DC at circuit output! what was that? was our circuit in defect? No, because this is an oscillator circuit and we were trying to measure DC voltage the output. There should be a waveform of AC voltage which should be measured at oscilloscope. Set up the oscilloscope and calibrated it using its internal calibration square wave out put.

Oscilloscope is calibrated and prepared to look at the output of the circuit.

Then connected the oscilloscope input signal probe to the circuit out put and the ground of the oscilloscope to the ground of the circuit using the alligator clip on scope probe. The circuit selection jumper had been set up to sin wave.

Oscilloscope probe and ground are connected at circuit.

Then started measurement for the first function sin wave.

The first functions sin wave is being tested.

After observing the sin wave on the screen, the jumper had been set up to triangular wave.

The second functions triangular wave is being tested.

After observing the triangular wave on the screen, the jumper had been set up to saw tooth wave.

The third functions saw tooth wave is being tested.

After observing the saw tooth wave on the screen, the jumper had been set up to square wave.

The fourth and final function square wave is being tested.

Then the circuit gain control or attenuation had been observed but adjusting the potentiometer in the gain control circuit using a screw driver and observed the behavior at scope screen. I observed that the gain control was working and was changing the output signal level from zero to maximum.

The circuit gain control is test by the gain control potentiometer.

By this way we checked all the project for proper functionality and working. Now is the time to fix this project board in appropriate box and bring it in use.


Here is the part 1 of this bolg post covering assembly detials:
Function generator assembly instructions part 1

Here is the part 1 video covering assembly details.