Building iPhone and iPad Electronic Projects

Chapter 5. Creating a Moisture Meter with HiJack

About This Chapter

Prerequisites

Read Chapter 1 and the end of Chapter 2 (the section on the techBASIC help system) if you need some help with techBASIC. Read Chapter 4 for general information about HiJack. In particular, iPads and late model iPhones need an external power supply for HiJack; see Chapter 4 for details.

Equipment

You will need an iPhone, iPod, or iPad running iOS 5 or later. You will also need a HiJack device from Seeed Studio, a Grove moisture meter (also available from Seeed Studio), and various common electronics parts like wires and resistors. See Table 5-1 for a complete parts list.

Software

You will need a copy of techBASIC or techBASIC Sampler.

What You Will Learn

This chapter uses HiJack, a device that supports an eight-bit A-D converter plugged into the headphone port, to build a plant moisture meter. This is a functioning example that shows how to use the technology introduced in Chapter 4 in a real-world sensor application.

Adding a Moisture Meter to the Tricorder

Back in Chapter 1 and Chapter 2, we explored the tricorder we all carry in our pocket. This project turns an iPhone or iPad into a quadcorder, hanging a HiJack A–D converter and sensor off the end and then using techBASIC to read it. We’re going to build a nifty moisture meter from off-the-shelf parts, as shown in Figure 5-1. Even the initial software is something you’ve seen before: we’ll start with the HiJack program from Figure 4-10 in ...