BCD to PWM

Dr_Doggy

Well-Known Member

• Oct 22, 2010

• #1

I found my 555 pwm circuit and a BCD counter and wanted to stick them together, in my diagram i used simple transistors to decode the resistors, note that i wired them in series to the Rpack would simulate a n^2 value for the bits,, but IDK how to wire them up properly, as far as i can get is that i need pnp transistors,, it worked good with relays but i'd prefer transistors, so its not so bulky, any ideas??

 

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Grossel

Well-Known Member

• Oct 23, 2010

• #2

All you need is a binary comparator with 2x4 bit input. One for the counter and one to control the output. Clock/counter will give pwm frequenzy

 

Brevor

Member

• Oct 23, 2010

• #3

A 4066 quad analog switch would probably work for you, Replace the 4 transistors with the analog switches.

 

Grossel

Well-Known Member

• Oct 24, 2010

• #4

Brevor said:

A 4066 quad analog switch would probably work for you, Replace the 4 transistors with the analog switches.

Click to expand...

Not mention any weaknes to analog switch, but as I see it would only provide 5 possible voltage combinations.

 

Brevor

Member

• Oct 24, 2010

• #5

Not mention any weaknes to analog switch, but as I see it would only provide 5 possible voltage combinations.

Click to expand...

In his circuit as it is drawn It would provide the same number of voltage combinations as the 4 transistors would.

 

Last edited: Oct 24, 2010

crutschow

Well-Known Member

Most Helpful Member

• Oct 25, 2010

• #6

An R-2R Ladder is often used for a digital-analog conversion since it requires only two resistor values.

 

Dr_Doggy

Well-Known Member

• Oct 25, 2010

• #7

Excelent Carl, can i feed that right in to my discharge pin?

 

crutschow

Well-Known Member

Most Helpful Member

• Oct 25, 2010

• #8

An R-2R ladder network is designed to generate a current output into a a virtual ground or very low impedance load to achieve good accuracy. Feeding its output into the discharge pin will reduce that accuracy since that's not a low impedance load.