Band-pass filter

Today lab session, we used the Oscilloscope to test the signal generators built built by Paul and Sven (as shown in Figure 1). However, one colpitts oscillator generated expected signal which is 7Mhz, the other one ,instead of producing 10Mhz, has a uneven output signal.

Figure 1: Signal generator Oscilloscope testing. 

After having a discussion and suggestion from the lab instructor, we decide to built the band-pass filter to detect our target frequency (ass shown in Figure 2). I spent hours to look at the combination of capacitors, resitors to peoduce the target 7Mhz and 10 Mhz band-pass filters. However, what I found was that the capacitor and resitors I needed for the circuit were'nt not avalable. Hence, we thought about buying it.

Figure 2: Band-pass filter diagram.

In the end of the lab, after considering the time limit and the current problem with the hand built signal generators, we decided that we will come back and use AD9850 DDS (see Figure 3) as the signal generators.

Figure 3: AD9850 DDS.

There are a few reasons make us choose AD9850 DDS instead of continuing building our own signal generator:

• AD9850 DDS is the ready chip. It is ready to use and hence, it can save us time.
• It is realative cheap around 8£ which is still under budget for this project
• It produces clean sine wave signal which important for detecting signal later
• It can be easily programme to change the frequency

However, there are some drawbacks that we need to deal with when using the AD9850 DDS;

• We need the Arduino to programme/control the AD9850. It means that they must come as a set of Arduino+AD9850 DDS to work.
• The combination of Arduino and AD9850 is relatively big.

Considering the advanatges of using the AD9850 outbreak some small drawacks using AD9850 brings, we have made the final decision that using the AD9850 as the signal generator.