Hello

So first let me explain what i am doing:
I'm triyng to build an exponential VCO with this project: https://www.allaboutcircuits.com/projects/diy-synth-series-vco/
I need a dual power supply so i have built this circuit (NE555 version) https://www.allaboutcircuits.com/uploads/articles/NVG555.jpg from this tutorial: https://www.allaboutcircuits.com/projects/build-your-own-negative-voltage-generator/

But now i have a few questions because i prefere to be sure of what i'm doing.

In the negative generator circuit i have three outputs: V+, V- and the ground (GND). Now my problem is how to link this to my VCO ?
I don't understand how to link the negative generator to OP-AMP of the VCO.

First i'm not sure to understand the schematics:

• Is all the op-amp of the "linear to exponential" circuit connected like this: VCC in the pin Vs+ / VEE in the pin Vs- ?
• Is all the op-amp of the "VCO" circuit connected like this: VCC in the pin Vs+ / GND in the pin Vs- ?

Then:

• Is the V+ output of the negative generator the VCC of the VCO ? (If it's true i need to do something because it's not 5V ?)
• Is the V- output from the negative generator the VEE of the VCO ?

You can find the schematic of the exponential VCO and the negative voltage generator in attachment.
Thank you in advance for your kind consideration of this request. English is not my native language so it's quite hard to speak with all the complicated vocabulary of electronics. So If something is unclear or further information is required to respond to a specific item, seek clarification and ask questions.

 

Welcome to AAC!
Vee is the most negative voltage, as provided by the V- pin of your negative generator. The V+ pin of that generator becomes the new GND.
All opamps in both the 'linear to exponential' circuit and in the VCO should have pin 4 connected to Vee and pin 8 connected to the most positive voltage (Vcc).
In the VCO only, R8 and R12 are now redundant. Wherever you see 'Vref' you connect to the new ground. Wherever you see the old 'GND' you connect to Vee.

 

Thank you a lot for your answer, that's very helpful !
If the V+ pin of the generator becomes the new GND for the VCO, so i have to connect pin 8 of all op-amps to the GND of the generator (because it's now the most positive voltage)?

 

Sorry, no. By the V+ pin of the generator I meant the 'more-positive-than-the-V-' pin , i.e the pin which is labelled 0V in the generator pic. That 0V is your GND, which sits about half way between the pin 4 and pin 8 voltages.

 

ok i was completely wrong, to sump up,
The 0 Volt in the generator is the 'GND' for "the linear to exponential" and "VCO"
The "V+" in the generator pic is 'VCC'
The "V-" in the generator pic is 'VEE'
it is correct ?
Thank you , (sorry i'm slow to understand)

 

Does this help?

I haven't shown the +5V supplying the Neg Gen.

 

Thank you for your prompt rely. Yes it helps it's very clear now. I understand how to build the circuit.
However I'm not sure to understand why the circuit requires different grounds and a VREF in the VCO, I need to think more about this.

 

I'm not sure to understand why the circuit requires different grounds and a VREF in the VCO

The VCO circuit as shown uses a single-polarity supply (Vcc,Gnd), with a centre-tap derived by R8/12 and called Vref.
The exponential circuit as shown uses a dual-polarity supply (Vcc,Gnd is the positive supply and Gnd,Vee is the negative supply.
It is a matter of making the two circuits compatible by re-naming the 'half-way' voltage and the lowest voltage in the VCO circuit. Thus the VCO 'Gnd' becomes 'Vee' and the 'Vref' becomes 'GND'.
The combination of the two power supplies (your +5V supply and the negative generator) provides voltages of +5V, 0V and -5V, so the 'half-way' voltage is 0V, making R8 and R12 redundant.

 

Thank you a lot for your very clear explanations. I Think I understood