Battery status system

CR123 is the battery type that will be used for the system, according to requirement CR-003. In the analysis of the CR123 battery type we want to examine a few different alternatives to ensure our design is within compliance of normal commercial batteries. This is important so the end user is not dependent on the battery producer to use our system.

The battery specification comparison can be found in the table below and is constructed from [38], [40] and [66]

Nominal voltage 3.0 Volts 3.0 Volts 3.0 Volts

Storage temp 40C to 60C N/A N/A

Operating temp -40C to 60C -40C to 60C -40C to 60C

Typical capacity

Typical weigh 16.5 grams App. 16g App. 16g

Typical volume 7.0 cubic

Table 8: CR123 battery specifications from different manufacturers

Figure 60: Discharge curve of the CR123 from GPBatteries [66]

Energy(J) = Amperhour·voltage·3600 (4) The total amount of energy in a Energizer CR123 battery can be calculated using (4) and is roughly equal to 12960J. This is assuming the voltage is constant around 2.4V (widest part of the battery characteristic), which we know is not always the case. This means that since the battery needs to deliver 18J of energy every time the plasma igniters needs to activate we can have a total of ^12960J_18J = 720 cycles roughly speaking. We also need to consider that we will lose some energy from the battery to the plasma igniter in form of heat to operate the different circuits. Another condition that will impact the amount of energy available for the plasma igniter is the temperature of the battery. In 60 we can observe that at -20^◦C the capacity is substantially lower than at 23 ^◦C. This implies that we need to take into consideration the temperature of the battery when trying to estimate its status. Furthermore we need to choose a boost converter that accepts a voltage range that is suitable for the CR123 battery characteristics.

When we have figured out what kind of voltage level that is reasonable as input to the boost converter and the rest of the circuits we must monitor the battery voltage. From Requirement SR-018 we know that the electrical system needs to deliver 9J at 350V to

LM3914

After some initial research we found the LM3914, which is a monolithic integrated circuit that is capable of sensing analog voltage levels to drive up to 10 LEDs. The initial thought is that since the circuit can trigger up to 10 LEDs we could instead provide a microcontroller with a binary word. That way the embedded software could notify the user about the battery status. The temperature range of the IC is also within range of our compliance.

The block diagram and specifications of the LM3914 can be found in [68]. After looking through the block diagram, we simulated parts of the circuit in LTSpice to verify its characteristics as you can see in Figure 61. We believe it is a possible solution, but we need to investigate the power consumption and integration with the rest of the system further before making a decision.

Figure 61: LTSpice simulation of LM3914 main circuitry

Analog to digital converter (ADC)

Another alternative is to use an ADC IC to read the battery voltage and use a micropro-cessor or another digital device to interpret and act upon the data.

The Least Significant Bit (LSB) voltage can be calculated using the equation below from [20]

LSB = V_{SP AN}

2^N (5)

Now, let’s consider the GPBatteries CR123 discharge curve (60). Our voltage span (V_{SP AN}) can be selected to be 3.3V and by using Equation 5 with a eight bit resolution we achieve a LSB of 0.0129V. This is voltage difference between each discrete output level (number of counts). For an eight bit resolution we get 2⁸ levels (counts).

The accuracy of the ADC is important because the CR123 discharge characteristics are quite sensitive. Quantization error is inevitable due to the output being discrete, but we wish to minimize the effect of it. Quantization error is the difference between the ide-al/theoretical value and the actual value. The maximum error is usually specified as 1/2 LSB in datasheets, so we want to minimize LSB, and we see from Equation 5 that this can be done by increasing the resolution.

Looking at a 8 bit ADC, MAX153CPP+, it has a power rating of 2mW when operating, but also offers a powerdown mode with only 5µW consumption. ADC is also a fairly com-mon part integrated in development boards and microcontrollers. Currently, alternative 2 is most desired because it does not need modifications and it is a widely available component.

Temperature sensor

Since the system is to be used in all kinds of environments(TR-003), we know that this affects battery capabilities. At this time we are considering using a temperature sensor that can be used together with the voltage reading. This way we will be able to estimate the battery capacity better.

Contents

5.3.2.1 NFC Module . . . 175

Chapter Introduction

This chapter of the bachelor thesis for the Spark remote firing system concerns the im-plementation of the proposed solution in the proposal section. In it, our prototyping and each discipline’s part of the implementation is addressed. For software, this means a user-friendly application running on an Android operating system programmed in C++

(back-end) and QML (front-end). This application has NFC and IP capabilities, and facil-itates the means by which an operator can pair receivers and control them over a network.

As described in section 4, the Make Decision functionality has been the primary focus of implementation. For electrical, the circuitry of the receiver unit is considered; due to time constraints, the custom PCB has not been used for prototyping. For mechanical, the casing of the receiver is addressed. At the end, we detail two prototypes that were constructed during the project; a third is not detailed in the same manner, as the rest of the implementation chapter constitutes this prototype as the final implementation of our proof of concept.

5.1 Software Components

The software implementation consists of the network and communication elements of the remote firing system, along with an Android mobile application (sender) to communicate with the receiver. The remote firing system contains numerous software components, which are positioned on both the receiver and sender. The receiver would be the remote firing device itself, and the sender would be an Android device running our mobile application to communicate with the receiver.

There are some similar software components present in both sender and receiver, such as the network interface, connection handler and the packet handler. These components provide a communication channel between both sender and receiver, along with the com-munication between multiple receivers within a local network.

Figure 62: Software components (sender) Figure 63: Software components (re-ceiver)

The network interface establishes the connection between sender and receiver, and the con-nection handler (also called heartbeat) is a pinging mechanism that checks if the concon-nection is alive or not. The packet handler is the process of packing, unpacking and transfering the data between senders through our peer-to-peer network. This process is explained in more detail in section 4.1.4.