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Here is a schematic for a possible solution. Since you still haven't said, I've assumed you are using the 5V version of the Q50 and that 8-bit resolution is sufficient. You will need to increase the PWM frequency if you want the settling time to be lower than a few seconds.

It is the 5V input version. Just checked.
8-bit is more than sufficient.

What coding specifically would go into arduino to control this?
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Preferably, you should use PID controller software. There is a standard one for the Arduino. What method do you intend to use to select the output voltage? If the device will be standalone, then I suggest a rotary encoder and LCD display.

The 5.6V zener diode in the schematic is intended to limit the voltage fed to the Q50 to 5V. However, the datasheet for the Q50 implies that if you run it with 5V supply when the output is lightly loaded, it will produced more than 5kV, which is outside its safe operating area. Therefore, until you have got the software right (in particular, the PID parameters), I suggest you use a lower voltage zener diode (perhaps 3.9V or 4.7V) in order to limit the supply voltage to the Q50 to a lower value.

Here's a variation of the circuit that provides better current limiting and avoids the need for a power resistor. You should put a heatsink on the BD435 transistor.


* Scan 151.JPG (109.66 KB, 1653x1165 - viewed 38 times.)
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The arduino will recieve data from matlab which measures the focus measure value from the lens. That part of the system has been done.
Depending on the value we need arduino to change the output voltage.

I still am unsure what the transistor does in the diagram.
Also the electro-optic lens needs the +/- ve connection, but on the diagram theres only one coming the hv multiplier.
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The transistor passes the power (up to 250mA) to the HV multiplier. The op amp cannot supply enough current by itself.

The high voltage output is on the right hand side of the schematic. The positive side is marked "+ 0-5 kV", and the negative side is marked Gnd. The negative side is common with Arduino ground. If you wanted negative output instead of positive output, then you would need to use model Q50N and change the arrangement of the voltage divider.
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The transistor passes the power (up to 250mA) to the HV multiplier. The op amp cannot supply enough current by itself.

The high voltage output is on the right hand side of the schematic. The positive side is marked "+ 0-5 kV", and the negative side is marked Gnd. The negative side is common with Arduino ground. If you wanted negative output instead of positive output, then you would need to use model Q50N and change the arrangement of the voltage divider.

Okay my bad, what i meant was that the lense has to electrode probes that would need the voltage going to. Can this just be divided from the output? I dont understand the 9V at the top section either.
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Please explain the voltage requirements for the lens. Have you a specification or datasheet for the lens?

The +9V is where you connect the incoming power. You need to provide 9V or a little more at 250mA. You can use the same supply to power the Arduino if the supply can handle the extra current for the Arduino + anything running from its 5V supply.
« Last Edit: April 01, 2013, 02:22:42 am by dc42 » Logged

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Please explain the voltage requirements for the lense. Have you a specification or datasheet for the lense?

The +9V is where you connect the incoming power. You need to provide 9V or a little more at 250mA. You can use the same supply to power the Arduino if the supply can handle the extra current for the Arduino + anything running from its 5V supply.

The lens operates between 2-3kV, but we aim to be able to control it with a system.

Can the roles of the resistors prior to the op-amp and the role of the op-amp be explained in more detailed?
The resistors coming off the HVM i am assuming is to make safe the connection back to arduino ground?

(sorry im quite a beginner trying to attempt a complex project)
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Can the roles of the resistors prior to the op-amp and the role of the op-amp be explained in more detailed?
The resistors coming off the HVM i am assuming is to make safe the connection back to arduino ground?

The 10K resistor keeps the op amp input at ground potential while the Arduino is initializing. Without it, the voltage on the op amp input would drift to +5v because of the input bias current of the amplifier, causing the unit to produce the maximum output voltage.

The 100K resistor and 0.1uF capacitor smooth the PWM to a steady voltage.

The 100M and 100K resistors between the HV output and ground form a voltage divider to convert 0 - 5kV to 0 - 5V, allowing the Arduino to measure the output voltage.
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Also the resistor and transistor after the op-amp i presume is to control input voltage to the HVM?
« Last Edit: April 13, 2013, 05:40:40 pm by domo » Logged

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This was the suggested circuit for using the HVM,
I dont understand why use a buffer?
« Last Edit: April 13, 2013, 05:40:09 pm by domo » Logged

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1. You need a buffer because an Arduino can only supply 40mA per output pin, whereas the 5V version of the HV multiplier requires up to 250mA.

2. However, there are very few op amps that can supply as much as 250mA output current. That is why I suggested using an op amp and NPN transistor as the buffer.

3. You cannot connect the input of the buffer direct to an Arduino output pin, because the Arduino does not have an internal DAC to drive any output pins with a variable voltage, and you must not try to drive the HV multiplier with PWM. That is why I included the RC network at the input to the buffer.
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1. You need a buffer because an Arduino can only supply 40mA per output pin, whereas the 5V version of the HV multiplier requires up to 250mA.

2. However, there are very few op amps that can supply as much as 250mA output current. That is why I suggested using an op amp and NPN transistor as the buffer.

3. You cannot connect the input of the buffer direct to an Arduino output pin, because the Arduino does not have an internal DAC to drive any output pins with a variable voltage, and you must not try to drive the HV multiplier with PWM. That is why I included the RC network at the input to the buffer.

Why can the HV not be driven by the PWM?

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PWM works when there is some averaging mechanism to smooth out the PWM. Electronic assemblies generally do not have this averaging mechanism. If you try to feed them with PWM'd power, they will generally not behave in the way you want, and draw high peak currents which are likely to damage them and/or the circuits driving them.

Some electronic assemblies provide a a separate PWM input. The HV multiplier you are planning to use does have the option of an external input for turning off the HV supply, but it is clear from the datasheet that this input is not intended for PWM.
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10-bit: 12-bit external DAC + possible op amp + emitter follower.

11-bit: 12-bit external DAC + possible op amp + emitter follower + 12-bit external ADC.

The "possible op amp" would be needed unless you are using the 5V version and it is lightly loaded.

When using a DAC, would that be connected to the Arduino output, and then to the rest of the circuit?
and im guessing the ADC will come before the HVM module? any examples on how to adjust the circuit, or what to add in to make these effective changes?

Also the op-amp i have, has 8 pins but only 3 is needed for the circuit (im presuming) but would i need to ground it too?

Also if another Arduino board was to be used (such as Due, which has a DAC) does that remove the need for an external DAC?

 
« Last Edit: April 06, 2013, 05:26:36 pm by domo » Logged

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When using a DAC, would that be connected to the Arduino output, and then to the rest of the circuit?

The DAC would be connected to the Arduino via SPI or I2C depending on which DAC you used. Its output would feed the non-inverting input of the op amp, in place of the R-C filter.

Also if another Arduino board was to be used (such as Due, which has a DAC) does that remove the need for an external DAC?

Yes. AFAIK the Due is still the only Arduino board that has an integral DAC.
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