SIMPLE DO-IT-YOURSELF ELECTRONIC PROJECTS
Digital Counters can be put to good use in analog emusic, for they provide a way to generate complex 'Gating' which can be used to synchronize a multitude of logic devices and DC controllers.
One of these logic devices, the 'Dual Synchronous Up Counter"( CD4520BM), offers a variety of applications. it can be put to good use for generating audio sounds and/or complex gating to drive, for example, drum machines and sequencers.Furthermore, it does not need any additional components: everything is there on the chip.
In the Audio mode, a square wave audio frequency (with a pulse -width ratio of 40%) applied to the clock input of the CD4520BM chip will generate 8 individual outputs which are the 8 lower octaves division of the Master frequency:
Example: Square wave Master frequency= 3520Hz (A7); Output frequencies = 1760Hz (A6), 880HZ(A5), 44OHz (A4),220hz (A3), 110HZ (A2), 55Hz (A1) and 27.5Hz (A0). This means, that with only one analog VCO as master frequency, you can have up to 9 VCO (1+8) at the output: a really fat sound...
Imagine what 4 of these chips can do to any analog modular 8 voice synthesizer...I personally use this configuration with my Oberheim SEM-1 Expander Systems (I have 5 SEM-1 Modules=10 VCO). With this chip, I now have the equivalent of 40 oscillators!
In the Sub-Audio mode , this chip can also be used to generate very sophisticated gates to synchronize envelope generators, drum machines and sequencers, provided that they accept a low +5V Gating : all clocks are a precise sub-division of the original clock.
Example : Master clock (with a Pulse-Width of 40%) = 128bpm ; Individual output clocks = 64 bpm, 32bpm, 16bpm, 8Bpm, 4bpm,2bpm,1bpm,0.5bpm. (Each clock output can , for example, trigger individual instruments of a drum machine or be used with a sequencer (EXT. Clock IN)
Note :As the chip is a DUAL counter, you can use the LEFT part of the chip for audio purposes (4 sounds+Master sound=5 sounds) and use the RIGHT part of the chip for complex clocking purposes (4 clocks + Master clock=5 clocks). However, if you want to use the chip in a "Master+ 8 outputs" configuration, you should patch externally the Out 4 A Pin to Clock B in.
1) Buy the CD4520BM chip at Radio Shack or any other company selling components : Cost= +/- $ 5.00
2) Buy a 16 Pin socket to accomodate the chip : Cost= +/- $ 0.50
3) Use a breadboard or buy a small PCB board with holes already pre-drilled :Cost= +/- $ 5.00 ?
4) Solder carefully the 16 Pin socket to the PCB board.
5) Wire all inputs and outputs with sufficiently long cables to reach the inside of the future patchboard or Jack Bay. (it is wise to solder the wires to the nearest holes adjacent to the pin number of the chip, then make a "blotch" of solder to connect).
Pins 16 to 9
Pins 1 to 8
Pin 1 = clock A input (to connect a Square Wave with a Pulse Width of 40%)
Pin 2= Enable A (+5V)
Pin 3=Out 1 (A)
Pin 4=Out 2 (A)
Pin 5=Out 3 (A)
Pin 6=Out 4 (A)
Pin 7=Reset (Ground)
Pin 8=Common Ground
Pin 9=Clock B input (to connect a Square Wave with a Pulse Width of 40%)
Pin 10=Enable B (+5V)
Pin11= Out 1 (B)
Pin 12=Out 2 (B)
Pin 13=Out 3 (B)
Pin 14=Out 4 (B)
Pin 15=Reset (Ground)
Pin 16= V+ (+5V)
6) Connect all the input/output wires (and grounds) to a jack-bay or patchboard : The lay-out should read :
(A) Clock in, Out 1, Out 2, Out 3; Out 4
(B) Clock in, Out 1, Out 2, Out 3, Out 4.
7) Insert the CD4520BM carefully in the 16 Pin socket: check if all pins are well inserted.( Beware : the notch (or the dot) on the chip should be pointing 'Upwards' on the PCB Board).
8) Use an analog or digital Multimeter , set it to the Ohm range, and test all pins and wires for bad connections or shorts.
9) Connect all +5V inputs to a +5V DC power supply (or a +9V DC battery).
10)Connect all grounds to the GROUND of the power supply (or the black wire of the 9V battery)
That's it : Total cost of the project= +/- $ 10.00 !
PROGRAMMABLE Divide by N Counter 4 Bit Counter
A more sophisticated counter, is the CD4526BM Programmable Divide by N 4 Bit Binary Counter (where N is a value from 1 to 15). The counter has 4 outputs : Out 4, Out 3, Out 2, Out 1(each output is a division by 2 of the previous stage). For example, if the rhythm settings are programmed for 4/4 and the clock input is 32 bpm, then Out 4 =16 bpm, Out 3= 8 bpm, Out 2= 4 bpm and Out 1= 2 bpm.
Usually, the Counter is programmed using a combination of 4 DPST toggle switches ( Binary ON=1, OFF=0). There is also a Stage Select Trigger Input for each stage. So, sophisticated rhythms can be easily pre-programmed using both binary switches or external pulse control.
By using 2 Counters simultaneously, one can achieve very fancy rhythms : 3 beats against 4, 4/4, 5/7, 6/8,3/8,9/8, 10/8,12/8 and so on. For example, to program a rhythm in 4/4, the first and the second counter are programmed to deliver a gate every 4 beats : binary switch 4=OFF, binary switch 3=OFF,binary switch 2 =ON, binary switch 1=OFF (decimal 4) (See 'Decimal values for Binary switches' and 'Truth Table')
Obviously, with both combination of binary switches settings and Stage Select Trigger inputs one can obtain very interesting rhythms combinations. For example, in the above 4/4 rhythm example, one can change the program of the sequence, using external pulse control, to obtain N/4 rhytms: 4/4,4/4,4/4, 8/4 (external pulse control on stage 1, every n cycle) or even 4/4,12/8,4/4,12/8 or any other rhythm from 1 to 15...