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negative voltage building problem

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rezaf

New Member
Hi everybody
I want to make a negative voltage to control the zoom & focuse of my security camera and control the negative voltage with MCU. I want one component that converts the positive to negative voltage with any need of other components. any one know that what component I must use ?????????
I used from MAX232's VS+ and VS- pins but it's capacitors and ISIS software's problems to control supply of MAX with MCU is a difficult for me .
thanks for your help .
 

MikeMl

Well-Known Member
Most Helpful Member
Source power supply?
Load voltage?
Load current?
What type of control? DAC on MCU? PWM from MCU?
 

rezaf

New Member
Re

Thanks
my camera's zoom and focuse input voltage are in range of 3~13 V DC and low current about 500 mA .with negative voltage Zoom- & focuse- with positive voltage reverse.I want when push one of zoom- and focuse- button that connected to MCU the MCU pin high, and activate the component that convert positive to negative voltage then the camera with output of that and GND will go to zoom- or focuse- .
 

ccurtis

Well-Known Member
500 mA is not a low current in terms of using inexpensive, inverting charge pump devices and circuits. Methinks you need a separate, negative power source followed by an adjustable, negative voltage regulator (switching or linear), or some other means to adjust the voltage. Some DC-DC converters have an isolated output (owing to an internal transformer), so they can be driven from an existing, positive power source to provide a negative power supply.

I am assuming from the info you give that the control voltage to the camera for the focus and zoom share a common ground with the rest of the cameras circuitry. This seems to me unusual since the focus and angle are driven by geared down motors which should have separate wires for the motors, making a strictly negative voltage source unnecessary. But, it is what it is.
 

rezaf

New Member
picture of my question

I have attached a picture to understanding the purpose. I previously do this work in 3 form (in picture) .1-with transformer with centre tapped and relays. 2-with MAX232 and relays 3-with four MAX232 . but now I don't have enough space for this works and ISIS don't permission to control VCC pin of ICs with other component. 500mA is based on guesswork and are lower. in back of camera are 3 terminal that named zoom com focuse .
thanks.
 

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ccurtis

Well-Known Member
You say that on back of the camera there are three terminals, but in your diagram there are shown four terminals. Could it be that two terminals are for Zoom and the other two for Focus? I can't read the terminal labeling on your diagram, it is too fuzzy.

Also, have you actually applied real voltages to the terminals to see that both Zoom and Focus functions work as you describe?

If so, have you actually tried the MAX232 devices to see if they can drive the Zoom and Focus motors?
 

rezaf

New Member
Re

sorry. the ISIS software dont have 3 pin terminal .one pin zoom one pin focuse and one pin com .I tested the MAX232 and worked .I think the camera only take order with this terminals and drive zoom motors with himself 12v supply .
 

ccurtis

Well-Known Member
Okay, the picture is getting clearer. So, to be sure, you don't need to apply a variable voltage to the zoom and focus. You only need to apply a fixed voltage, but alternating between negative and positive. Right?
 

rezaf

New Member
yes. for example, with a +8.5v the camera get zoom+ and with a -8.5v the camera get zoom- too for focuse .
 

ccurtis

Well-Known Member
Assuming yes to my above question, I see a solution. The MAX232 has a TX output which goes positive or negative depending on the state of the TX input. Since you already know that the V+ and V- of the MAX232 can drive a motor, then the TX out can also drive a motor. Your MCU can drive the direction of the motor by outputing to the TX input, high or low. The only problem is that you have to turn both voltages off to stop the motor. The MAX222 has an additional shutdown input that can be driven by the MCU to disable to the TX output to turn a motor off. So, then what you end up with are two MAX222 devices. The TX of one MAX222 controls ZOOM. The TX of the second MAX222 controls FOCUS and each of the shutdown inputs turn the motors off. What do think?
 

rezaf

New Member
the MAX232 exept the TX and RX have two pin with VS+ and VS- name that I used from the second and with MCU control the supply of MAX and turn it on and off to control output voltage because when the MAX turn on always have output on all pins .
I can't use TX pin because that pin permanently go high and low depend on input.
 

rezaf

New Member
there are 4 MAX in picture. when focuse- the MAX 1 turn on by MCU and with pin VS- and com(GND) the camera get focuse- . when focuse+ the MAX 2 turn on by MCU and with pin VS+ and com(GND) the camera get focuse+ . and reverse .
 

ccurtis

Well-Known Member
the MAX232 exept the TX and RX have two pin with VS+ and VS- name that I used from the second and with MCU control the supply of MAX and turn it on and off to control output voltage because when the MAX turn on always have output on all pins .
I can't use TX pin because that pin permanently go high and low depend on input.
Yes, that's why I suggest the MAX222 because it has an additional input (SHDN) to turn the TX pin off. It is not good to disable the V+ and V- output voltages of the MAX232 by using the MCU to supply +5V power to the MAX232.
 

rezaf

New Member
very thanks .I go to exam the MAX222 if my problem don't solved I ask again from you .
thanks for spend time for me .
 
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