555 voltage controlled oscillator question

Please read the datasheet of NE555. NE555 have have 2 comparators and 3 voltage resistor. Voltage control pin5 was connected to comparator with 2/3 reference voltage. Your 0-5V was not enough amplitude for 2/3 VCC of NE555. That's the reason that it does not affect frequency of NE555.

 

NE555 can still function on +5V on its VCC and therefore matched with yun 0-5V input voltage.

But if your installing the NE555circuit to +12V supply. You can place a series resistor and 5.1V zener diode for the supply of 5.1V of NE555 VCC. This will solve matching of 5V vco input. Swap connection of pin7 and pin 3. Then pin 7 will be your open collector output. But you need a pullup resistor of around 1k and connect to +12V and pin 7. Pin 7 oscillator output will swing from 0.7V to 10V.

 

555 is a timer IC. Use 566 which is a VCO IC. It can generate triangle and square waveform, and you can change the frequency by feeding a variable voltage.

https://www.egr.msu.edu/eceshop/Parts_Inventory/datasheets/lm566.pdf

 

Rleo is wrong; you can operate a 555 with pin 5 over quite a wide range. But it's not a very ideal VCO - the frequency vs. voltage graph is not linear, and an increasing voltage causes a decreasing frequency (over most of the range, at least). You can improve it by adding external components - see http://www.electroschematics.com/7170/wide-frequency-range-555-vco/ (I have not tried and don't necessarily endorse that design.)

The 566 is a very old device and appears to be obsolete.

There are many devices that can be used as VCOs. A popular and easy-to-use one is the CD4046B (see http://www.digikey.com/product-detail/en/CD4046BE/296-2052-5-ND/67295). It is an old device, but is still used, and manufactured by three companies: NXP (formerly Philips), ON Semiconductor (formerly Motorola) and Texas Instruments (who acquired it from National Semiconductor).

Avoid versions of the 4046 that include 74 in the name; most of these require a 5V supply voltage. The 4046 operates from supply voltages up to 15V (some versions can tolerate 18V).

The 4046 WILL be damaged by voltage surges and spikes on the automotive +12V power supply rail; you NEED to include clamping (using a zener diode and/or voltage suppressor with series resistors) and/or an automotive voltage regulator if you're operating ICs in an automotive environment, which is harsh (Google load dump). Regulation is a good idea anyway, since supply voltage variations will affect the VCO behaviour somewhat. Clamping may also be needed on the control voltage, to avoid damaging the high-impedance control voltage input of the 4046.

The 4046 is easy to use as a VCO because it has two auxiliary resistors that can be used to determine the frequency range covered by the full range of control voltages. For example, if your control voltage range is 0~10V, you can set the 4046 to produce a corresponding frequency range of 10~1000 Hz, or 100~200 Hz, or 10,000~10,010 Hz, or 10,000~15,000 Hz, or whatever you need. There is a single timing capacitor (as in most VCOs).

It also has a very high-impedance control voltage input, which is helpful if you want to add filtering on the control signal because it will not cause a voltage offset.

I suggest you get all of the following data sheets, because different manufacturers provide different types of detail:
NXP: http://www.nxp.com/documents/data_sheet/HEF4046B_CNV.pdf
ON Semi: http://www.onsemi.com/pub_link/Collateral/MC14046B-D.PDF
Texas Inst.: http://www.ti.com/lit/ds/symlink/cd4046b.pdf

And buy a few devices and play around with different values for C, R1 and R2 to get the idea of how to use it.

As I said, there are other VCO devices available. Have a look at Digikey's selection table at http://www.digikey.com/product-search/en?FV=fff40027,fff80205&stock=1&quantity=1&pageSize=250 but beware, most of the options are SMT (surface mount technology). If you filter those out, there aren't many options left; most of those are variants of the 4046.

If you want any more specific advice, you need to tell us more about your project.

 

My mistake.KrizBluenz was correct. Pin6 that tied with pin2 will be a sawtooth voltage from charging and discharging of capacitor and within the range of threshold voltage 0-5V pin5.. NE555 will still oscillate even with +5V or lower voltage with corresponding change in frequency.

 

Haha! Yep. You could fix this, but since the control voltage works backwards (lower voltage = higher frequency), there's not much point. The usefulness of pin 5 on a 555 is limited to making siren circuits. You'll like the 4046. Just be careful not to damage it - keep the inputs within the supply rails, and buffer the output if you need more than a few milliamps from it.

 

You can't vary the duty cycle by feeding the output through a comparator - the output is a square wave with a duty cycle of 49~51%. You would have a similar problem with the 555 circuit - the main output is a square wave, and the waveform at pins 2 and 6 would vary in amplitude and average voltage as you varied the control voltage.

You might be able to do what you want by triggering a monostable with a time constant that's controlled by the VCO voltage in conjunction with the duty cycle control voltage.

Perhaps if you describe your project in detail we will be able to offer some suggestions.

 

The amplitude of the triangle-ish wave will vary depending on frequency. So you would have to either vary the resistor in the integrator, or vary the comparator threshold, to compensate.

If you need variable duty cycle independent of frequency, a good option would be the two-op-amp "integrator + Schmitt trigger" oscillator configuration, using a transconductance amplifier to drive the integrator. Actually there was a circuit posted here recently that did that - see https://www.electronicspoint.com/threads/which-capacitor-is-best.269126/#post-1612612

You wouldn't need most of that circuit. The important bits are IC2A, C4, IC3C and IC1 (I give the designer extra points for gratuitous use of a 555 in a proper circuit). The signal on IC3's output is a triangle wave with fixed amplitude (swings between about 5V and 10V, determined by the 555's thresholds) with a frequency determined by the current going into pin 1 of IC2A. Let me know if you want to go down that road.

I thought the injectors had to be synchronised to the rotation of the engine...?

 

Connecting anything to pin 6 or pin 7 would not be recommended by the manufacturer and it might not work properly with a different brand of 4046. But if that doesn't worry you, and your load has a very high input resistance, it may be OK. It's a lot simpler than using an integrator or low-pass filter.

 

If you want a VCO that can generate arbitrary duty cycles, it's probably best to start with one that generates a triangle or sawtooth wave with constant amplitude (and therefore, variable steepness). If pin 6 or 7 of the CD4046 has a suitable signal, you can use that, but I'd be concerned that different brands might have different signals on those pins. That's just because no manufacturer says anything about what those pins do, other than the fact that you connect a capacitor between them.

If you have an oscilloscope, you should check the waveforms on those pins to confirm that at least one of them is a triangle or sawtooth. I've never looked into it myself. But you might want to check CD4066es from several manufacturers.

Passing the square wave through an R-C filter will not give you a triangle or sawtooth wave, so your duty cycle control voltage will not map linearly to duty cycle. You could use an integrator or a resetting ramp generator, but in either case your current will need to be made proportional to the frequency, otherwise the amplitude of the triangle or sawtooth wave will vary with frequency. That's why I suggest it's best to source the triangle or sawtooth waveform directly from the VCO.