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By Clive Seager* In Part 4, we used our Schools Experimenter board to control DC motors, solenoids and servos. In this, the final instalment of the series, we look at adding infrared remote control and voice recording capabilities. For more advanced experimenters, we also show how to build a sound detection circuit that complements the simpler light and temperature circuits described in Parts 2 & 3. IN THIS ARTICLE you will learn: • how to use infrared remote control; • how to record and play back sounds; • how to detect and respond to sounds. Many indoor projects lend themselves well to infrared remote control, so for the first project, we’ll show you how to add an infrared receiver to your board that will work with a TV-style remote control. We’ll then add an external voice recorder module and * About the author: Clive Seager is the Technical Director of Revolution Education Ltd, the developers of the PICAXE system. 90  Silicon Chip show you how to record and play back a sound clip via remote control. To get started, let’s look at the infrared remote control side of things. Infrared remote control Every infrared remote system consists of two parts: a transmitter and a receiver. There are many different protocols for sending infrared data, with most major manufacturers opting for their own “standard”. The PICAXE system uses the Sony infrared remote control (SIRCS) protocol, allowing it to be used with a normal TV-style remote control. All universal, “one-for-all” style infrared remote controls can be set up to control Sony brand equipment and therefore will work with this project. It’s just a matter of programming the remote with one of the Sony equipment codes provided in the accompanying instructions. For example, the TVR010 remote control featured here must be programmed with the unique code C-2-1-2. Note that it’s also possible to make your own transmitter using a second PICAXE-08M chip, instead of buying a universal remote. Check the “PICAXE Infrared Remote Control” article (featuring “Rudolph the Red-Nosed Reindeer”) in the November 2004 edition of SILICON CHIP for more details. The PICAXE-08M requires only four siliconchip.com.au additional components to receive infrared transmissions, as shown in the simplified circuit of Fig.1. This circuit (minus the PICAXE chip) is easily constructed on a breadboard and then connected to the experimenter board, as illustrated in Fig.2. Make sure that the DIL switch (SW2) positions 3 & 4 are OFF and that 1 & 2 are ON. Each infrared transmission is 12 bits long and is produced by modulating a 38kHz carrier signal (see Fig.3). A TSOP4838 infrared receiver module detects the infrared signal with the use of a photodiode. The signal is then demodulated (ie, the carrier is removed), before it is fed into the PICAXE-08M chip for decoding. A block diagram of the internals of the TSOP4838 receiver module is shown in Fig.4. The BASIC program in Listing 1 shows how to use the infrain2 command to read data from the infrared receiver module. Once an infrared transmission is received, the program uses familiar commands to switch one of the three LEDs on the experimenter board on or off, depending on which of the first six numeric keys on the remote control is pressed. Note that within the Sony protocol, the number transmitted by the remote control is actually one less than the number you would expect from the button (eg, pressing button 4 actually transmits the data value 3!). Task – write a program that makes the green LED flash to indicate the number of the numeric key pressed (ie, five flashes for key number five). Keys other than 1-9 should be ignored. Fig.1: this simple circuit adds infrared support to the PICAXE-08M. A Vishay TSOP4838 infrared receiver module detects and demodulates the infrared data stream, which is then fed into the microcontroller on input 3. Fig.2: here’s how to wire up the infrared receiver circuit on the breadboard and connect it to the School’s Experimenter. Recording & replaying sounds A significant number of functions are required to record and play back sound on a computer system. First, the sound must be picked up by a microphone and amplified. It must then be filtered and converted from analog to digital form. It can then be stored in memory ready for playback. To play back the sound, it must be retrieved from memory, converted from digital to analog format, amplified and then fed to a loudspeaker. This simplified description holds true for all digital sound recording systems and one of the key requirements for such a system is lots of memory space. Even short sound clips require a lot more memory than is available in a low-cost microcontroller like the PICAXE-08M. siliconchip.com.au Here’s what the above circuit looks like assembled onto the breadboard. Also shown is the TVR010 infrared remote control mentioned in the text. November 2005  91 Fig.3: basics of the SIRCS protocol, showing the composition of each serial transmission. A logic “1” is represented by a 1.2ms burst of the 38kHz carrier, whereas a logic “0” is represented by a shorter 0.6ms burst. Each bit is separated by a gap of 0.6ms. Fig.4: this diagram reveals the basic functional blocks inside the TSOP4838 infrared receiver. As well as the actual PIN (photo) diode, it includes amplifier, discrimination and demodulation circuits to reconstruct the original digital data, which appears on the “OUT” pin. One way of providing sound recording capabilities on a simple microcontroller-based system is to use a dedicated recording chip with inbuilt memory, such as one of the ISD5100 series Chipcorders (www.isd.com). These devices can store from 2-16 minutes of voice-quality sound. Unfortunately, these chips are quite difficult to interface to the PICAXE-08M. A much simpler and cheaper solution is to “hack” into a pre-assembled recorder module. These are available in many forms, from keyring note-takers to surplus modules originally destined for children’s toys. Generally, these modules are easily modified to work with PICAXE microcontrollers. One such module is shown in one of the photos. It is supplied with two pushbutton switches (record and play), a speaker, a LED and a battery holder, all attached to a small PC board via flying leads. The following description deals exclusively with the PPM155 module but other types are readily interfaced to the PICAXE micro in a similar manner. For example, the Oatley VRM1 25s voice recorder (www.oatleye. com) would probably be suitable, as would the 45-Second Voice Recorder project described in SILICON CHIP, in May 2005. Note: although designed for 4-cell (6V) operation, the PPM155 module described here operates satisfactorily from a 4.5V supply, as will most other 6V modules. Of course, we cannot guarantee that all modules will work from a 4.5V supply, so check for suitability before “hacking”! In some cases, a separate supply may be required for the module. Before going any further, install batteries in the recorder’s holder and try it out to make sure that it works properly. This will also give you the opportunity to discover how it works – before hacking it! You will note that with this module, the “record” switch has to be held down to record, while the “play” switch only has to be pressed momentarily to play back the sound. The LED should light while recording is taking place. Hacking the recorder module The first ‘‘hack” involves cutting off the battery holder so that the whole project can use the Schools Experimenter battery pack. Cut the red and black wires close to the battery holder, leaving plenty of length from the PC board side for connection to our project. The second job is to replace the “play” and “record” switches with outputs from the PICAXE-08M chip. Each switch is connected to the module via two red wires; one goes to “0V” and the other to the input of the speech memory chip. You need to identify which of the two wires goes to the speech memory chip and connect it to output 1 (for the “play” switch) or Fig.5: here’s how to connect the voice recorder module. If you’ve already constructed the infrared receiver on your breadboard, then don’t disassemble it – just add this circuitry as well. Note that you’ll need to solder short single-strand jumper wires to the end of each of the recorder’s flying leads so that you can plug them into the small holes in the breadboard. 92  Silicon Chip siliconchip.com.au The sound recorder module offered by MicroZed may differ from the unit shown here but should be just as easy to interface to the PICAXE micro. This unit features “record” and “play” buttons, a LED, a miniature speaker and a battery holder, all attached by short lengths of wire. All functions are performed by a single IC, which is hidden beneath a mound of black epoxy. Strangely, even the through-hole components are mounted on the copper side of the board! output 2 (for the “record” switch) of the PICAXE. The correct wire is easily identified by using your multimeter to measure the resistance between the negative (black) battery lead and the two wires soldered to the switch assembly. The “0V” wire will measure zero ohms to battery negative, so it can be ignored; the other wire is the one to be connected to the PICAXE. Your completed breadboard layout should look something like Fig.5. As you can see, we’ve added 330W resistors between the two PICAXE outputs and the module’s switch inputs, which help to protect against accidental wiring mistakes! Make sure that DIL switch (SW2) contacts 1 & 2 on the experimenter board are now switched off. The program in Listing 2 will record 10 seconds of sound and then immediately play it back. The playback is then constantly repeated, with a 1-second delay between loops. It is important to note how the outputs work; the module switches are “active low” and so we have to switch the PICAXE outputs high at the start of the program and then pulse them low to activate the module. The final step in the project is to combine the infrared circuit with the siliconchip.com.au sound recorder circuit. Task – write a program so that the record and playback features are triggered by a key press on the infrared remote control. If you combine this project with a servo-operated “puppet” on output 4 (see Pt.4 of this series for servo information), you could build a very interesting animatronics project! Sound detection In previous articles, we looked at how to measure light (using a lightdependent resistor) and temperature (using a DS18B20 sensor). Unfortunately, sound is not as easy to detect with a PICAXE-08M chip, as it requires considerably more than a simple “single component” solution. The main problems to be considered when designing a simple sound detection circuit are as follows: (1) While electret microphone inserts are ideal due to their low cost, they produce a very small signal that requires amplification; (2) The background noise level can vary considerably and so some form of calibration is required; and (3) Some noises, such as a hand-clap, are very quick and so could easily be missed by PICAXE programs. Fortunately, these problems can all be overcome at low cost, using an Par t s Lis t IR receiver & sound recorder 1 TSOP4838 infrared receiver module 1 TVR010 remote control (or any universal remote, see text) 1 PPM155 20s sound recorder (or similar, see text) 1 4.7mF 16V electrolytic capacitor 1 4.7kW 0.25W 5% resistor 3 330W 0.25W 5% resistors Note: the remote control (part no. TVR010) and TSOP4838 sensor (part no. LED020) are available individually or in a combination pack (part no. AXE040) from MicroZed, see www.picaxe.com. au for more information or phone (02) 4351 0886. Microzed can also supply the PPM155 sound recorder module. Sound detector 2 BC548 transistors (Q1 & Q3) 1 BC558 transistor (Q2) 1 1N4148 diode (D1) 1 electret microphone Capacitors 3 470nF polyester 1 1nF polyester Resistors (0.25W, 5%) 1 220kW 2 4.7kW 1 100kW 1 100W 1 10kW 1 5kW miniature trimpot (VR1) 1 50kW miniature trimpot (VR2) November 2005  93 Fig.6: the sound detection circuit uses a handful of low-cost parts. The first stage amplifies the signal from the microphone, which is then clipped, peak detected and finally buffered to provide a 0-3V output. electret microphone together with three common transistors and a few resistors and capacitors, as shown in Fig.6. This circuit will produce an analog output signal of 0-3V that can be read by the analog input (eg, input 4) of the PICAXE-08M. It also includes a time-delay feature that extends the period of the loudest signal. The program in Listing 3 demonstrates how to use the readadc command to read the signal from the detection circuit connected to input 4 and light the red LED when a loud sound is heard. Note that contact 4 of the DIP switch (SW2) must be in the “off” position. As before, the circuit can be constructed on your breadboard, using Fig.7 as a guide. We’ve used multi-turn trimpots for VR1 & VR2, as they’re easy to insert in the breadboard. However, ordinary single-turn miniature trimpots could also be used. Important: never force over-sized component leads into the breadboard holes. Solder short lengths of singlestrand jumper wire to large leads first to allow easy insertion. How the detector works Sound is sensed by a low-cost electret microphone, which for typical speech levels produces an output of about 1mV RMS at a distance of about 60cm. This means that we can expect signal levels of about 1-3mV from the microphone. The electret microphone is based on a special type of Field Effect Transistor (FET), physically constructed to convert vibrations (from sound or physical contact) into an electric signal. It is a polarised device and must be connected the right way around; the negative (-) lead is easily identified as it is connected to the external metal can. The output from the microphone is coupled to the base of the first transistor (Q1) via a 470nF capacitor. This transistor acts as an amplifier, providing a gain of 25 over the 300Hz-30kHz frequency range. The result is a larger (25-75mV) signal on the collector, where it is picked off by the wiper of sensitivity control pot VR1 to feed the following stage. Like the sound waves that it represents, the AC signal applied to the second stage consists of constantly rising and falling (alternating) voltage levels. In order to detect a signal (and therefore a sound) level above a set amplitude, it is necessary to establish a reference point on the signal from which to measure. To this end, the second-stage transistor (Q2) is biased to cut-off and amplifies only negative-going signals. The resultant positive-going signal at the collector causes D1 to conduct, thus charging the 470nF capacitor at its cathode to the peak signal level. The third transistor (Q3) is configured as an emitter follower. Its job is to buffer the signal from the 470nF capacitor, providing a low-impedance output for driving external circuitry. The signal at the output rises faster than it falls, proportional to the value of the 470nF capacitor at the base of Q3. We can therefore say that this capacitor defines the “delay time” that the highest sound level is present. Using the 470nF value shown, the Fig.7: the sound detection circuit calls for a much more complex breadboard layout than used previously and should prove a challenge! Make sure that you don’t mix up the two different transistor types and check their orientation – the flat side must face the right way around. Also, check that you have the banded (cathode) end of the diode pointing the right way. 94  Silicon Chip siliconchip.com.au decay time of the output signal is approximately 0.5 seconds. Increasing the capacitor to 2.2mF provides a decay time of approximately two seconds. Adjustments Initially, set the sensitivity control (VR1) to minimum (wiper towards the positive rail). Next, set your multimeter to read DCV and connect it between the output (emitter of Q3) and the 0V rail. Now adjust VR2 to a reading of just above 0V on your meter. This slightly positive bias of a few millivolts helps to avoid a “dead band” in the response of the detector. The sensitivity control (VR1) is now increased to a suitable level for the project. Typical speech at about 50cm from the microphone will give a DC output of about 1V peak. A handclap should produce an output of about 3V peak. As mentioned earlier, you’ll find that the signal is present for longer than the noise that causes it, as dictated by the value of the capacitor in the base circuit of Q3. And finally . . . We hope that this series of articles has given you some confidence in programming and working with PICAXE microcontrollers. Although this is the final in our “PICAXE in Schools” series, there will be more PICAXEbased projects in future issues. Happy SC experimenting! Program Listings Listing 1 Listing 2 main: infrain2 if infra = 0 then red_on if infra = 1 then yellow_on if infra = 2 then green_on if infra = 3 then red_off if infra = 4 then yellow_off if infra = 5 then green_off goto main init: high 1 high 2 record: low 2 pause 10000 high 2 play_back: low 1 pause 100 high 1 pause 10000 pause 1000 goto play_back red_on: high 0 goto main yellow_on: high 1 goto main green_on: high 2 goto main Listing 3 red_off: low 0 goto main main: readadc 4,b1 if b1 > 100 then bang goto main yellow_off: low 1 goto main bang: high 0 pause 1000 low 0 goto main green_off: low 2 goto main TAKE YOUR PIC Picaxe.com.au DISTRIBUTOR: MicroZed.com.au Developed for students, & professional performance makes PICAXE the most easy-to-use micro ever: PICAXE “programmer" is two resistors and a 4.5V battery! PHONE 1300 1300 735 735 420 420 8.30-4.30 AEST Mon-Fri FAX 1300 735 421 24 Hours ALL PICAXE ITEMS ON OUR SHELVES! STOCKISTS siliconchip.com.au In AUSTRALIA: altronics.com.au (Retail and Mail Order) oatleyelectronics.com School Electronic Supplies In NEW ZEALAND sicom.co.nz surplustronics.co.nz (School orders only – John - 03 8802 0628) November 2005  95