Project Overview

Introduction

The aim of the project was to produce a circuit capable of transmitting energy wirelessly from one circuit to another (via an “antenna” made of two copper-wire coils).

The block diagram outlining the basic concept of each element of the project can be seen in fig. 1.

Figure 1: Project block diagram

Week 1 (3rd of February 2017)

During the first project week, the transmitter and receiver circuit designs were discussed and agreed upon by all group members. The initial circuit design chosen for the transmitter is shown in Fig. 2a, while the circuit diagram for the receiver is shown in Fig. 2b.

Fig. 2a) transmitter circuit 

 Fig. 2b) receiver circuit

The circuit was simulated using PSPICE. The two circuits were constructed separately on two separate SK10 boards and tested afterwards.

Transmitter circuit

Two MOSFETs (IRF540) were included in the design, acting as an oscillator by connecting eight cascading capacitors as a “tank” circuit (connecting in parallel with the transmitter coil).

Table 1: Transmitter circuit component list

Component (with value)	Quantity
Resistor (10kΩ)	2
Resistor (94Ω)	2
Resistor (1k)	1
MOSFET – IRF540	2
Inductors (8.6μH)	2
D4148 diode	2
Inductor coil (0.674μH)	1

The following formula was used to calculate the required frequency:

The receiver circuit was then tested using the AC voltage provided from the function generator, with the expected values being retrieved. However, the transmitter circuit was not performing as required, as there was no current supplied to the inductors within the circuit.

This meant that in order to progress further with the project, a simulation needed to be performed in PSPICE to detect why the inductors were not being supplied with the required current. Doing so would also allow any other problems to be identified and dealt with accordingly.  

Receiver circuit

Table 2: Receiver circuit component list

Component (with value)	Quantity
Resistor (1k)	1
Capacitor (6.8nF)	8
LM7805 voltage regulator	1
D4007 diode	4
Inductor coil (1.235μH)	1

The receiver circuit consisted of a receiver coil and a capacitor in parallel, which was used to absorb the electrical energy from the transmitter circuit, while also charging the AC voltage it had received. This was then connected to a full-bridge rectifier, to change the voltage from AC to DC. The low-pass filter (consisting of a capacitor and a resistor) ensured only lower frequencies were allowed to pass through to the LM7805 voltage regulator (which reduced the output voltage from 30V to 5V). 

Week 2 (10th of February 2017)

The transmitter circuit was simulated in PSPICE to identify and solve the current supply problem. The connection between the output of the oscillation circuit to the “tank” circuit was found to be incorrect, therefore leading to a lack of current flow to the inductors. This problem was fixed by altering the wire connections, as they were not connected in the right way initially.  However, no frequency was measured at the output of the oscillation circuit, while there was also no waveform displayed on the oscilloscope. The recorded voltage output from the oscillation circuit was also DC (and not AC as required).

Figure 3: Simulation schematic for transmitter circuit using PSPICE

It was also important that the number of turns for each coil (transmitter & receiver) were discussed and calculated using the appropriate formula. The group decided to follow a concept that had already been observed in previous modules (electromagnetism).

The inductive loops were calculated using the formula below: 

The two coils were then put together in the same style, with a different number of turns required for both. A similar style to which these loops were made can be observed from the image in figure 4.

Figure 4: Chosen inductive loop design

Once this problem had been solved, the group planned to continue working on the simulation in PSPICE to solve any other potential circuit problems. 

Week 3 (17th of February 2017)

Some issues were encountered during the third lab session with regards to the transmitter circuit design. Both MOSFETs used in this circuit became too hot as a result of a larger than required amount of current running through them. This meant that a drain resistor needed to be added in series to deliver a lower operating current. The existence of such a high current value meant that even a low input voltage caused both MOSFETs to overheat (around 4 or 5 volts made the components start to burn).

While the introduction of said resistors (0.66kΩ) reduced the amount of current flowing from the drain of the MOSFET, although this was not able to reduce the amount of heat dissipated in both transistors. In order to solve this problem, a “heat sink” was used instead to ensure both MOSFETs were able to operate without overheating.

Due to the fact that the necessary results were not obtained from the transmitter circuit, it was important to consider other potential designs that were able to produce the required frequency oscillation. The group made the decision to perform more research to find an alternative design to the one currently being used. It was clear at this stage that the current design would not provide the necessary energy transfer required. 

Week 4 (24th of February 2017)

Transmission circuit design changes

The fourth project week required more research to be performed to find a new transmission circuit design. After the fourth group meeting, several different designs were discussed, although it was agreed that one particular design appeared more effective than most. The group decided the best course of action was to include a 555 timer to produce the required oscillation, while also using a BJT and MOSFET as a voltage amplifier (and a high-speed switch). The newly chosen circuit design can be observed in figure 5a. 

Figure 5: Circuit diagram for new transmission circuit design

The timer produced an oscillation as required, while the frequency was calculated using the formula.

Copper wire coil design change

It was also discovered that the method used to produce the copper wire coils was not effective, meaning that a new design had to be considered instead. This newly chosen design can be observed in figure 6.

Figure 6: Newly chosen copper wire coil design

The inductive loops and number of turns were calculated using a new formula.

Turns ratio was 1:1 for both coils, so that N_T = N_R

The new circuit was simulated step by step, starting from the transmitter circuit. The simulation produce the expected values when calculated from the aforementioned formula to get the required output frequency from timer. The Inductors from the previous design were removed and replaced with a short circuit before adding the coils.

The receiver circuit was also put together on PSPICE, while a linear transformer (with a 1:1 turns ratio) was added. 

Calculate the     for the MOSFET :

Design inductance loop:

The simulation was successful and provided the required outputs. The schematic diagram can be observed in figure 7, while the results of the testing stages can be observed in figures 8, 9 and 10.

Figure 7: Design simulation using PSPICE

Figure 8: INPUT Voltage and OUTPUT Voltage

Figure 9: INPUT voltage, OUTPUT voltage from 555 Timer and the Final OUTPUT Voltage

Figure 10: INPUT voltage for TX-coil and OUTPUT voltage through RX-coil

The circuit was then transferred to an SK10 board to test the input/output voltage and current. This testing can be observed in figure 11.The results of the test were as expected. The circuit was working effectively and was therefore able to transfer electricity from the transmitter to the receiver. 

A demonstration of this can be observed in the video.

Figure 11: Testing the circuit

Receiver circuit design changes

The only changes that occurred in the receiver circuit were changed to the values of the components within (C3 & C4 were changed to 2.2nF & 10μF).

Figure 12: circuit diagram for Receiver circuit 

Week 5 (3rd of March 2017)

The final lab session involved simply soldering the transmitter and receiver circuits on to two separate veroboards. All necessary tests were performed during the previous week, meaning no extra calculations or design changes were required with regards to circuit composition.

The receiver circuit was soldered on to the veroboard as required and produced the appropriate results. However, the transmission circuit was not producing the same output as before, which lead to the group’s decision to simply connect the circuit to a small SK10 board instead. Both circuits were then tested together and everything was working as expected.

Both circuits were then placed inside two small black boxes, with the round copper wire coils working as an antenna between the two. Images of the soldering process can be seen in fig. 13, while the final assembly of the two circuits together in black boxes can be seen in fig. 14.

Figure 13: Soldering the component on veroboard

Figure 14: Final project assembled

video shows the final testing of the project after assembled into 2 different boxes

Week 6 (10th of March 2017)

The sixth project week required the final preparations to be made for the bench inspection day to ensure the product was presented appropriately in its final form. This involved the refinement of the poster design, while also ensuring that the logbook and other necessary documents were completed and up to date.  The group also used this week as an opportunity to come together and discuss the final circuit design, ensuring all participants were up to speed with how the circuit is able to achieve the necessary energy transfer.

The first draft of the poster can be seen in figure 15, while the final draft can be seen in figure 16. The design had to undergo small changes to make sure that people reading the poster were not overwhelmed with large amounts of text.

Figure.15: 1st draft of the final poster 

Figure.16: Final image of the poster