I'm trying to revive an old motorized zoom & focus lens (Pentax c14zme-2) I got off eBay. The focus and zoom share a common ground and take a +/-12V 50mA DC supply:
The only documentation I have is a sticker on the cable and all the circuitry is sealed inside the lens case. I haven't been able to find any similar projects on the web, but I do know that a 9V battery attached to the cable whirrs the motors.
What's the best way of controlling the lens with a UNO using a 12V mains supply?
Can I just treat it like two separate motors and wire it to, say, a dual HG7881 controller board. Would the common ground blow it up? I don't need to zoom and focus at the same time so I could write the software to just run one motor if necessary.
Since the motors share a common ground, should I just use a single DC controller with a relay to switch between the blue and green outputs? Are there any better alternatives to the relay?
The yellow and black wires control the iris and (I think) need 12V max 35mA. How can I provide this? Or should I just use another DC motor controller board?
looking at focus for example it appears that you apply +12volts DC to move NEAR and -12volts to move FAR
I suggest you get a power supply with + and - 12volt DC output and experiment
also find out what happens you you reach the limits of focus and zoom - does the device automatically cut out or the motor continue to run possibly burning out the motor or overloading the power supply
if it works you could use two SP3T (single pole 3 throw) to control the zoom and focus
if you cannot find a SP3T relays (they appear to be mainly electro mechanical) in each case you can use two relays one to apply +12volts and the other -12volts but take care that you don't switch both on at the same time
What's the best way of controlling the lens with a UNO using a 12V mains supply?
Well you need to be able to reverse the polarity of the voltage, so with only a single ended supply you need a H-bridge circuit. Either made from an IC or two relays, three if you want to control both motors one at a time.
you need a power supply that has both +12 and -12 VDC
the application does not appear to be swapping VDC and ground to get a 'reverse' connection like one would expect from an H-Bridge.
you put in +12VDC the motor is connected to to ground on a fixed leg.
and the motor 'sees' positive, or higher voltage on the +12 leg.
you connect -12 and the motor 'sees' the higher voltage on the GROUND and therefore runs in the opposite direciton
we do not know the workings of the internal circuitry and if you attempted to run both motors at the same time, there could be issues.
of course, it could be a dead simple DC motor connection. but without schematics it does not leave me comfortable.
dave-in-nj:
you need a power supply that has both +12 and -12 VDC
the application does not appear to be swapping VDC and ground to get a 'reverse' connection like one would expect from an H-Bridge.
That was also my first thought. But then I asked myself where would a camera get -12v DC from. It seems to me much more likely that it is just a simple DC motor and the OP's comment "but I do know that a 9V battery attached to the cable whirrs the motors." seems to confirm that.
Robin2:
That was also my first thought. But then I asked myself where would a camera get -12v DC from. It seems to me much more likely that it is just a simple DC motor and the OP's comment "but I do know that a 9V battery attached to the cable whirrs the motors." seems to confirm that.
you have a common ground so how would it be possible to apply +12v to focus and -12v to zoom
unless the switches were interlocked so both could not be pressed at the same time?
Robin2:
That was also my first thought. But then I asked myself where would a camera get -12v DC from. It seems to me much more likely that it is just a simple DC motor and the OP's comment "but I do know that a 9V battery attached to the cable whirrs the motors." seems to confirm that.
...R
I have to agree. but, like I said, I am not comfortable in telling someone to connect power to a device that has specific markings.
+12V and -12V are as simple as an LM7912 and an LM7812 .
then putting a pair of diodes on the line. feed it with one and it moves one way, feed it with the other and it moves the other way.
it is very possible that all this is inside of the device and there is a simple toggle that would complete the circuit.
looking at the simple schematic from the PENTAX manual seems to point to the opposing diodes being the deciding factor on the motor direction.
+12V and -12V are as simple as an LM7912 and an LM7812 .
Not from a single 12V supply they are not.
looking at the simple schematic from the PENTAX manual seems to point to the opposing diodes being the deciding factor on the motor direction.
The diodes seem to be on a limit switch. The only puzzle is that block that says CB. I can't see that as being any active circuit because their is no power to it, only the motor power, so could it just stand for "connection block"?
I don't see anything not to try using relays to control this.
A quick experiment with a HG7881 and a 12V DC power supply shows that I can control the zoom in both directions, so it probably means that there are just DC motors inside the c14zme lens. I also discovered that the HG7881 will also open and close the auto iris (aperture).
After Christmas is over, I'll order a relay to allow me to switch between zoom and focus. In the meantime, I will busy myself with getting a camera attached to the lens.
