Fullscreen HTML5Med Res (??MB)HTML4

By Clive Seager* Last month, we programmed our Schools Experimenter board to respond to digital and analog inputs. This month we’ll see how to use a sophisticated sensor for temperature measurement and have some fun playing mobile phone ring tones! In this article you will learn: • how to make sounds and play tunes; • how a for...next loop operates; • how to connect and use a digital temperature sensor. Sounds in electronic projects are usually generated with an electromechanical or piezo buzzer. We’ll describe only the piezo type here, as they use much less power than the electromechanical types and are well suited for use in battery-powered circuits. A typical piezo buzzer contains two main parts: a piezoelectric transducer and its driving circuit. The piezo transducer consists of a polarised ceramic material bonded to a metal disc. A voltage applied to opposite sides * About the author: Clive Seager is the Technical Director of Revolution Education Ltd, the developers of the PICAXE system. 68  Silicon Chip of the disc will cause it to flex, so by applying a varying voltage, it can be made to vibrate and produce an audible sound. The built-in driving circuit in a buzzer generally applies a voltage that varies (or “oscillates”) at a single frequency, resulting in a monotonous, irritating tone. In conjunction with the sound command, PICAXE micros can generate a voltage at an output pin that oscillates at a programmable frequency. By connecting a piezoelectric transducer (without the inbuilt driver circuit) to that pin, we can therefore make our own buzzer for signalling purposes – and much more. Making sounds In use, three numbers must follow the sound command. The first is simply the output pin number that is to be driven and on the Schools Experimenter board, this will always be output 2. The second number is the desired pitch of the sound and can be between 0 and 127. As one might expect, a higher number generates a higher frequency signal. The third number is the length of the sound in approximately 10ms steps. The simple program in Listing 1 shows how to use the sound command. In this example, three sequential tones of equal duration are produced. Listing 2 shows how the three lines can be combined into a single command to save PICAXE memory space. Note that on the Schools Experimenter board, the piezo transducer and green LED share the same output (output 2), so the green LED will flicker as the sound is being generated. For…next loops Often it is useful to repeat a section of BASIC code a number of times. For example, if you wish to flash the yellow LED (on output 1) five times, you can use a for...next loop as shown in siliconchip.com.au Fig.1: the digital output from the DS18B20 temperature sensor connects to input 4 of the PICAXE micro via the header socket (H1), as shown here. The sensor also requires power (+V) and ground (0V) connections and a 4.7kW pull-up resistor. Listing 3. In this example, variable b1 (b for “byte”) is used as a counter to keep track of the number of loops completed. Task – write a program that flashes the green LED 10 times when the switch on input 3 is pressed (you might need to look at last month’s article about inputs for a reminder). We can use the same for…next structure to make the piezo play every possible note using the sound command, as shown in Listing 4. The second for…next loop in this example shows how to repeat the scale in reverse by using a step value of -1 (the default step value is +1). Fig.2: here’s how to wire up the sensor using a small solderless breadboard. The jumper wires can be purchased in pre-cut lengths, or you can make your own with solid-core alarm cable and wire strippers. is lifted (a “birthday box”, perhaps). As described last month, the program makes use of the LDR to sense light level, allowing it to play the tune only at the appropriate moment. Two numbers follow the play command, both of which can take the value 0 to 3. The first number represents the tune (0 = Happy Birthday, 1 = Jingle Bells, etc). The second number can be used to flash LEDs connected to output 0 and/or output 4. We will not use this function in our experiments, so the second number should always be 0. Playing your own tunes The tune command is used when you want to compose your own tunes or import them using the Programming Editor, as we’ll see shortly. The tune command has the following syntax: TUNE LED, speed, (note, note, note...) where: • LED is a variable/constant (0 -3) that Playing built-in tunes The sound command is great for making simple “beep” noises but is not well suited for playing musical tunes. Instead, the PICAXE-08M offers the play and tune commands for this purpose. These musical commands operate on output 2 only, so unlike the sound command, the play and tune commands do not need an output pin number. The play command is used to play one of the four internally preprogrammed tunes, which are: Happy Birthday, Jingle Bells, Rudolf the Reindeer and Silent Night. For example, the program in Listing 5 could be used to play a tune when the lid of a box siliconchip.com.au The 10-way header socket (H1) allows you to connect external circuits to the Schools Experimenter board. A solderless breadboard provides a convenient base on which to construct your circuits. July 2005  69 Fig.3: import RTTTL tunes or create your own with the Tune Wizard, included in versions 4.0.1 and later of the PICAXE Programming Editor specifies if output 0 and/or output 4 toggle at the same time as the tune is being played. This can be used to flash LEDs but is not used in our experiments and should always be 0. • speed is a variable/constant (115) which specifies the tempo of the Par t s Lis t 1 DS18B20 temperature sensor IC 1 4.7kW 0.25W 5% resistor 1 10-pin SIL header socket 1 breadboard & jumper wire Where To Buy Parts The DS18B20 sensor can be ordered from MicroZed and their resellers, see www.picaxe.com. au for more information. Single-in-line (SIL) header sockets are available from Altronics (Cat. No. P-5390). These are supplied in 40-pin sections but are easily cut down to the desired size. Breadboards and pre-cut jumper wire packs are available from major kit suppliers. Jumper wires of any length can also be made using solid-core telephone or alarm cable and wire strippers. tune; and • note, note, etc, are the encoded musical note data. A detailed explanation of these parameters is beyond the scope of this beginner’s series. More information can be found in the PICAXE BASIC Commands manual. We also published details in the “PICAXE the Red-Nosed Reindeer” project (SILICON CHIP, September 2004). A good way to get a feel for the tune command and its capabilities is to import a ready-composed tune in the form of a favourite mobile phone ring tone. It’s actually quite easy to include ring tones in PICAXE programs. Let’s see how. Importing ring tones With a little help from the Programming Editor and its Tune Wizard, any monophonic mobile phone ring tone can be imported and automatically formatted for use with the tune command. Ring tones must be in RTTTL (ring tone text transfer language) format for use with this system. These are available from a number of internet websites, including Revolution Education’s site at www.picaxe.co.uk An example ring tone in RTTTL format is given in Fig.4. The first step to importing a ring tone is to highlight its text in Internet Explorer (or any text editor if you have downloaded it as a file) and use the Edit -> Copy function to copy it to the Windows clipboard. Next, select PICAXE -> Wizards -> PICAXE-08M Tune from the Programming Editor’s main toolbar. This will open the “Tune Wizard” screen (see Fig.3). To import the tune data, simply select Edit -> Paste ring tone. Finally, click the large “Copy” button to copy the formatted tune command complete with ring tone data into your BASIC program. As a matter of interest, the program in Listing 6 provides similar functionality to that in Listing 5 but uses the tune command instead of the play command. Important: in Listing 6, we’ve divid- Fig.4: Star Wars Theme Tune In RTTTL Format Star Wars Theme: d=4,o=5,b=125:1a#,1f6,8d#6,8d6,8c6,1a#6,2f6,8d#6,8d6, 8c6,1a#6,2f6,8d#6,8d6,8d#6,2c6,8f,8f,8f,2a#,2f6,8d#6,8d6, 8c6,1a#6,2f6,8d#6,8d6,8c6,1a#6,2f6,8d#6,8d6,8d#6,1c6 70  Silicon Chip We found that the jumper wires were a little loose in the socket, so we plugged a 10-way header into the socket first and then soldered our wires to that to ensure reliable connections. ed the note data for the tune command over several lines but in the Programming Editor, all note data must appear on a single line. Task – import a ring tone and write a program that will play the tune when the switch is pressed and the light level (sensed using the LDR) is low. Digital temperature sensor Last month, we used the on-board light-dependant resistor (LDR) and some simple programs to measure relative ambient light levels. In theory, we could use a thermistor (temperature sensitive resistor) and a similar scheme to measure temperature. However, thermistors are typically non-linear devices and our measurements would need considerable manipulation to give accurate results in degrees Celsius. An easier way is to use a DS18B20 digital temperature sensor IC. These devices contain an accurate temperature measurement circuit, with a digital output for direct interfacing to our PICAXE chip. The DS18B20 sensor’s digital output connects to input 4 of the PICAXE via the 10-way header socket (see Fig.1). If you haven’t already installed this header, then you should do that next. Rather than plugging the sensor pins directly into the header, it is easier to plug it into a small external breadboard. Connections between the breadboard and header can then be made with solid-core wire, as depicted in the accompanying photograph and on Fig.2. As shown, a 4.7kW resistor is also required for correct operation. Note that as input 4 is already used by the LDR, it must be disconnected from siliconchip.com.au Program Listings Listing 1 main: sound 2,(50,50) sound 2,(80,50) sound 2,(120,50) pause 1000 goto main Listing 2 main: sound 2,(50,50,80,50,120,50) pause 1000 goto main Listing 3 main: for b1 = 1 to 5 high 1 pause 100 low 1 pause 100 next b1 end Listing 4 main: for b1 = 0 to 127 sound 2,(b1,20) next b1 for b1 = 127 to 0 step -1 sound 2,(b1,20) next b1 goto main Listing 5 main: readadc 4,b1 if b1 > 80 then play_tune goto main play_tune: play 0,0 goto main Listing 6 main: readadc 4,b1 if b1 > 80 then play_tune goto main Silicon Chip Binders REAL VALUE AT $12.95 PLUS P & play_tune: tune 0, 6,($AA,$85,$43,$42,$40,$8A,$C5, $43,$42,$40,$8A,$C5,$43,$42,$43,$C0, $65,$65,$65,$EA,$C5,$43,$42,$40,$8A, $C5,$43,$42,$40,$8A,$C5,$43,$42,$43,$80) goto main P Listing 7 main: readtemp 4,b1 debug b1 pause 100 goto main Listing 8 main: readtemp 4,b1 if b1 > 25 then too_hot if b1 < 15 then too_cold temp_ok: low 0 high 1 low 2 goto main too_hot: high 0 low 1 low 2 goto main too_cold: low 0 low 1 high 2 goto main These binders will protect your copies of S ILICON CHIP. They feature heavy-board covers & are made from a dis­ tinctive 2-tone green vinyl. They hold up to 14 issues & will look great on your bookshelf. H 80mm internal width H SILICON CHIP logo printed in gold-coloured lettering on spine & cover H Buy five and get them postage free! Price: $A12.95 plus $A7 p&p per order. Available only in Aust. Silicon Chip Publications PO Box 139 Collaroy Beach 2097 Or fax (02) 9979 6503; or ring (02) 9979 5644 & quote your credit card number. Use this handy form Enclosed is my cheque/money order for the on-board circuits by moving position 4 of the 4-way switch (SW2) to the “off” position (leave all other contacts in the “on” position for now). The program in Listing 7 is almost the same as the LDR test program from last month, except that we’re using the readtemp command here instead of readadc. The readtemp command reads the temperature value from the DS18B20 sensor, which is then displayed on the computer screen with the aid of the debug command. The final program this month (Listsiliconchip.com.au ing 8) demonstrates how your system can act as “cold-warm-hot” indicator, using only the DS18B20 temperature sensor and the three on-board LEDs. Task – write a program that plays a musical tune when the temperature drops below 20°C. $________ or please debit my  Bankcard   Visa    Mastercard Card No: _________________________________ Card Expiry Date ____/____ Next month Signature ________________________ Next time around, we’ll look at controlling devices that move. Motors, servos and solenoids are all on the menu, so start looking through that SC junk box for motors to salvage! Name ____________________________ Address__________________________ __________________ P/code_______ July 2005  71