Week 4- Set back

In lab hours

This week we combined each part of our circuit that was responsible to us separately and tested its function. We rebuilt the circuit we obtained on a breadboard to another two strip boards in order to make the whole system easier to carry. The circuit is shown below in figure 1.  Two solar panels and the little port on Tp4056 that could be connected to the main electricity are used to charge the battery pack. When switched on, the battery pack would then generate the power into the amplifier circuit.  

Figure 1

As we expected to charge the phone we only need to plug it into the circuit, but it did not work. When we plugged it into an old iPhone 5 that is damaged but still could tell if it is being charged for testing, the phone reacted as its screen lit up, however, the battery kept dropping. 

%%%The video of the Phone reacted to the charger is presented in the next blog%%%

Possible reasons

After doing some research, we found it seems that it is for practical purposes impossible to make a truly universal charger using any combination of unchanging shorts or resistors on the USB charger or target device data lines because we are contending with manufacturers who are attempting to stop us doing exactly what we are trying to do.

For example, Apple implements a number of charging control schemes using various combinations of resistor dividers, arranged so that only a "matching" power supply and target equipment will work together. While arguments could be advanced that such arrangements allow optimum charging performance.

We later used a DC source and generate different values to see if we could charge the phone and the phone still did not react to the input. Probably we are not providing the phone with its specified values of voltage and current.

The USB we have purchased is a 2.0, SMT type A and has 4 pins in total, two of them represent GND and the voltage input, while two in the middle are data pins as shown in figure 2. We have tried multiple ways to connect the pins aiming to charge the phone without making data transmission in between but those all did not work out. The voltage between pin Vcc and GND have also been tested and revealed to be exactly the same as the output voltage provided by our circuit.

We then drew a conclusion that the failure of us trying to charge the phone could be because the data pins are not connected to the phone. There exists a small chip on top of the charging wire of the iPhone charger. As a result, though we could short circuit two data pins and connect it to the phone, it would not be charged when the charger is not verified. 

Figure 2

Next 

1. See if the charging circuit would work on other electronic devices, for example, a lamp. 

2. We have decided to focus more on the paperwork of the project and meanwhile, keep looking for the potential solution to the problem we have encountered.