Fullscreen HTML5Med Res (??MB)HTML4

This simple project produces a 64-note melody using just a 3-pin IC in a TO-92 plastic package, plus a few external parts. Six different ICs are available to give six different melodies, whilst a seventh chip produces a medley of tunes. By BERNIE GILCHRIST : s i h t d l i Bu T ABLE 1 shows the range of melody and medley ICs that are available for this project. A separate kit can be constructed for each melody required or the melody can be changed simply by swapping the IC. It should also be possible to change ICs using a 2-pole 2-position switch. Power for the circuit is derived from a single 1.5V cell but there is provision for an external 3-12V supply as well. The sound level produced by the small loudspeaker specified is quite impressive and can be reduced if necessary, as described later. At the heart of this project is a UM66TxxL low-power CMOS IC, part of a series designed for use in door bells, telephones and toys. This IC is an LSI (large scale integration) device which includes a ROM (read only memory) that is programmed with the note scales and rhythm codes. The oscillator and control circuitry is also built into the chip. The output from IC1 is a modulated rectangular waveform which is almost equal to the supply voltage in amplitude; ie, slightly less than 1.5V peak-to-peak. The required sound is achiev­ed by varying the frequency and width of the pulses. The output from IC1 appears at pin 1 and drives transistors Q1 and Q2 which operate as a Darlington output stage to drive an 8Ω loudspeaker. Resistor R2 is used for supply voltages greater than 3V and protects both Q2 and the loudspeaker from excess current (see Table 2). The 1µF electrolytic capacitor connected between Vdd (pin 2) and Vss (pin 3) is used to decouple the supply to IC1. This prevents the relatively high switching current in the output stage from interfering with the operation of the IC. D1, R1, R2 and LED 1 are used only if the supply voltage is 3V or more. These parts can be omitted if the circuit is to be powered from a 1.5V battery and R1 and R2 replaced by wire links. D1 protects the circuit if the external supply voltage is acci­ dentally reversed, while R1 and LED 1 together form a 2.3V regulator to limit the supply voltage to the IC (3.3V max). Table 2 shows the suggested values for R1 and R2 for exter­ nal supply voltages of 3-12V. Note that the 1.5V battery must be removed if you intend using an external supply. Assembly Fig.2 shows the parts layout on the PC board (code ZA-1324). You can install the parts in any order 1-Chip Melody Generator 80  Silicon Chip D1 1N4007 EXTERNAL BATTERY OFF S1 ON PARTS LIST R1 SEE TEXT 1k Q1 BC549 1.5V 2 A LED1 GREEN  1 50VW IC1 UM66T 3 1 B 1 PC board, code ZA-1324, 78 x 33mm 1 8-ohm 0.2W loudspeaker 1 AA single cell battery holder 1 SPDT slide switch 1 countersunk screw & nut (to secure battery holder) R2 SEE TEXT 8W SPEAKER C E Q2 BC337 B C Semiconductors 1 UM66TxxL melody generator IC (IC1) - see Table 1. 1 BC549 NPN transistor (Q1) 1 BC337 NPN transistor (Q2) 1 1N4007 silicon diode (D1) 1 5mm green LED (LED 1) E K B K A E 3 2 1 C VIEWED FROM BELOW MELODY GENERATOR Fig.1: the melody is generated by IC1 & this drives Darlington output pair Q1 & Q2 which in turn drive the loudspeaker. Capacitors 1 1µF 50VW PC electrolytic Resistors (0.25W, 5%) 1 1kΩ 1 R1 - see Table 2 1 R2 - see Table 2 TABLE 1 IC Type Melody Catalog Number UM66T01L Jingle Bells + Santa Claus Is Coming To Town + We Wish You A Merry Christmas K-5502 UM66T05L Home Sweet Home K-5504 UM66T09L Wedding March (Memdelssohn) K-5506 UM66T19L For Elise K-5508 UM66T32L Waltz K-5510 UM66T33L Mary Had A Little Lamb K-5512 but be sure to use the correct part at each location. Use wire links for R1 and R2 if you are going to power the circuit from a 1.5V battery, other­wise refer to Table 2 for the values of these components. Note that using a link for R2 will give the maximum output from the speaker but the battery life will be quite short. Alternatively, you can increase the battery life at the expense of output level by installing a low value resistor for R2 (eg, 10Ω). Take care when mounting the transistors. Do not push them too far down into the board because the leads spread and this may damage the connections inside them. Check that all polarised parts have been oriented correctly before applying power. These include the diode, transistors, IC, LED and the electrolytic capacitor. The LED leads are easy to identify – the cathode (K) lead is the shorter of the two. Although LED 1 is not intended to operate as a power indi­cator, it could also be used for this purpose if you are using an external (3V or greater) supply. All you have to do is reduce the value of R1 so that the LED current is about 5-10mA. The values shown for R1 in Table 2 give a current of about 1mA (ie, not enough to light the LED), so just divide the value shown for a given voltage to obtain the current Where to buy the kit This project was designed by Dick Smith Electronics who own the copyright on the PC board. Com­plete kits are available from all Dick Smith Electronics Stores or by mail order from PO Box 321, North Ryde, NSW 2113. The price is $9.95 plus $3 p&p. Please quote the relevant catalog number when ordering – see Table 1. required. Do not use a red LED for LED 1, as its forward voltage drop will be only about 1.8V (as opposed to 2.3V for a green LED). Once all the parts are in, install the battery and switch on. If everything is correct, the circuit will immediately start playing back the tune programmed into IC1. If it doesn’t, switch off immediately and check for SC wiring errors. S1 1.5V AA CELL TABLE 1 Supply R1 R2 1.5V link link 3V 560W link 6V 3.3kW 10W 1W 9V 6.8kW 22W 1W 12V 8.2kW 27W 5W D1 R2 R1 A EXT BATT 1uF LED1 K IC1 1 2 3 1k Q1 Q2 SPEAKER Fig.2: this wiring diagram shows all parts in position but note that some parts can be left out if power comes from a 1.5V battery. December 1993  81