555 Voltage Controlled Oscillator

RE: 555 Voltage Controlled Oscillator

msk167 — Sat, 05 Aug 2023 20:07:12 GMT

Dear 555 timers group.

I am interested in building this vco ramp generator with the neat voltage control circuit.

I am having some difficulty seeing how this new op amp controlled circuit replaces the voltage divider constant current source. I get that there is a replacement but it looks like the 555 connections are slightly modified.

Could you please send a schematic that shows the op amp and two transitor control circuit connected to the 555 circuit.

Thank you.

msk167

RE: 555 Voltage Controlled Oscillator

Jan Cumps — Thu, 30 Jun 2022 11:27:18 GMT

I ran your design through the Vivado tools, with Spartan-7 selected as FPGA.
Synthesized schematic:

Implemented:

readable PDF.

[View:/cfs-file/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-81f30b38-3084-4f3c-9506-43e63572ae92/synthesis_5F00_schematic.pdf:640:360]

[View:/cfs-file/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-81f30b38-3084-4f3c-9506-43e63572ae92/implement_5F00_schematic.pdf:640:360]

RE: 555 Voltage Controlled Oscillator

genebren — Mon, 13 Jun 2022 15:36:50 GMT

Great blog. I am very impressed with the linearity of the V to F. Working with a commercially available synthesizer which I was attempting to control the VCO from an external DC control voltage, I was somewhat disappointed in the periodic frequency shifts while tuning the circuit. It is nice to see what you were able to achieve here.

RE: 555 Voltage Controlled Oscillator

shabaz — Mon, 13 Jun 2022 14:27:02 GMT

Nice! I would not have guessed it would become a VCO, and that's a great range, more than 10:1.

I can guess fairly well (I think) where you are going with this, because I had a similarish need myself a while back, although I didn't blog about it because I didn't get to any decent point, my VHDL knowledge is really poor. My VHDL implementation did something, but there were enough grey areas in my understanding that I couldn't feel confident in what I was implementing was what I intended.

In my case it was for a radio project, and eventually I used a ready-made clock synth chip, which still irritates me, because I really wanted to get it working with a homemade PLL.

RE: 555 Voltage Controlled Oscillator

Jan Cumps — Mon, 13 Jun 2022 10:51:24 GMT

you may be able to guess where I'm going for part three.

Inject DC offset?