Wednesday, July 18, 2007

Low bit manip

I woke up with this simple idea in my head. It seems to be such a simple idea, in fact, that i should have thought of this a while ago. But anyway. It revolves around manipulating the output lines of a 4040 counter that drive a resistor ladder. In the schematic, R1-5 are twice the value of R6-8 (preferably within the 100kΩ - 200kΩ range). The cap is 0.22uF and the pot is 2MΩ.

For the time being, i am using only four bits, corresponding to the clock input (bit 0, LSB), Q1 output (bit 1), Q2 (bit 2) and Q3 (bit 3, MSB). By manipulating which line is going into which part of the resistance network, various waveforms can be achieved quite easily. This technique is expandable to a higher bit depth. However, there is an intrinsic speed limit; the speed of the input clock signal for the 4040 must be doubled for each bit added to the network.

4 bit sawtooth. you can clearly see the 16 steps.

by inserting an inverter stage in every bit line,
the shape of the waveform is reversed.

bits 2 and 3 share the bit 2 line.

bit order reversal.

bits 0 and 2 are swapped.