A Videologich Homecam bought second hand off Ebay.
It has a Sharp LZ24BP CCD sensor and is powered via a USB connection.
There are a couple of things I am going to change on this cam.
It has a built in microphone, which I won't need,
so this will be unsoldered from the board and the cable to it removed.
There is also a Green LED on the front that lights up when the cam is plugged into the USB port.
I might see if I can change this to a Red one and put a switch on the circuit to turn it off.
It might be handy for illuminating the eyepiece area on the scope when swapping Barlow lenses.
Removal of the microphone was straight forward.
The solder holding the microphones two legs in place was heated, gently, with a soldering iron and removed from the board.
I then plugged the cam into the computer to check that everything worked as it should.
It Did!
The same steps, as above, were taken with the removal of the LED.
I may add another Red LED and switch to this cam at a later date.
The modification came about after help from a few members of the QCUIAG group.
Armed with the specification sheet for the Divio NW801 (Cheers Steve) and clear pictures found on Howard Cripe's website for the Vcam CU98 modification, I started off by trying to establish a connection to the Sharp LR36685.
Knowing which pins to use on the Divio NW801 was a great help in tracking down the connections.
After finding the pins on the LR36685, I contemplated an attempt at a pin lift on this chip but it's close proximity to one of the 10 pin board connectors put me off.
It was then I realised that the boards connections could be a good target for a mod.
The circuit I've used.
The Amp-off part of the circuit will be added at a later stage.
The circuit I made is a copy of Howard Cripe's Vcam Circuit. I have used 10K resistors instead of 15K and a 4066 instead of a 4016. Everything else, exept the way it's connected to the cam, is the same. I had some success with this circuit but experienced a few problems after mounting the cam in a suitable box, I have now opted for a simpler circuit. See further down the page.
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Sharp LR36685 This picture shows which pins to target. Pin 22 is the shutter pin. Pins 15 and 23 are for the frame transfer pulse. |
DIVIO NW801 The pins on this chip are as follows: |
You can see one of the 10 pin sockets, that join the two boards together, above the LR36685. On the main board we have two 10 pin right-angled plugs, which attach to the sockets on the CCD board. It's the back of these pins that I have cut and attach wires. The pictures below show the pins I have cut.
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Transfer Pulse Connections. |
Shutter connection. |
No pin lifting with this modification.
After checking the conections between the Divio NW801 and the Sharp LR36685 and found the correct pins to cut, I snipped through the right-angle wires to break the connection. I gently heated the pins attached to the main board and removed them, this left holes ready to attach the wires for the modification board. Wires were also attached to the back of the pins that plug into the CCD board. You can see in the pictures below that it's a lot easier than a pin lift mod.
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Wires attached to the main board. |
Wires attached to the pins. |
The 5v needed for the LX circuit was taken from the rear of the USB connector.
The main Long Exposure modification complete and ready for testing.
I tested this cam with K3CCD Tools and it worked straight away with all the default settings.
Success!
This will be done at a later stage.
20 Second Dark Frame
Slight amp-glow evident in top right corner and only a few hot pixels.
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30 Second Dark Frame Amp-glow evident in top right hand corner and a fair amount of hot pixels. |
50 Second Dark Frame Amp-glow getting brighter. Amp off modification might have to be made for exposures of this duration. |
The following images were taken in a darkened room. Only the glow from my computer monitor is lighting up the room. The streak of light in the centre of these images is a gap in my blinds letting in a small amount of street light. When the lights are off I can't see my guitars hanging on the wall.
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5 x 10 second exposures. |
5 x 10 second exposures with darkframe subtracted. |
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5 x 20 second exposures. |
5 x 20 second exposures with darkframe subtracted. |
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5 x 30 second exposures. |
5 x 30 second exposures with darkframe subtracted. |
There are a few hot pixels visible in the 30 second exposures, even after the darkframe has been removed. There is no amp-glow evident in these images but it could show on a realy dark site.
I've used a small Aluminium case for this webcam.
A hole has been drilled at one end of the box big enough for the plastic lens holder to protrude through.
This is held in place with plenty of Epoxy Resin.
A cut down 'T' ring has been bolted and glued to the front of the case.
The thread on this 'T' mount is quite slack and I can screw on an M42 extension ring without any problems.
I can now use my collection of SLR lenses with this webcam.
A female 9 Pin 'D' connector is used at the back of the case for both the USB and control signals.
A hole has been drilled on the underside and a bolt, with a quarter inch 'Whitworth' thread, is attached to the inside of the hole and held in place with Epoxy resin.
This allows the cam to be attached to my Star tracking drive or a standard tripod.
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Problems!
There only appears to be one of the two interlaced frames been successfully captured by the computer.
The exposure is definitely brighter; so, the circuit is working, partially.
Everything worked fine out of the box, so, somewhere between then and now, something has worked loose.
Time to check all connections again.
I have found that the connection to pin 3 is at fault and the cause of the problem. I de-soldered this wire and connected it direct to pin 2, Similar to the SC1 modification, this worked and I managed to get some normal integrated LX frames. I have since disassembled the Homecam to check that it will still work as a normal webcam, it does. I am now going to rebuild the webcam with a much simpler SC1 style circuit.
The final simplified circuit.
After completely rebuilding the camera and re-designing a simpler circuit, the Homecam is now ready for some serious testing. There is now only two connections to the parallel port, there is a third for the Amp off mod but this isn't in use yet. I now have a switch option for normal or LX mode as in the SC1 modification. Both frames are now triggered by pin 2. I have added a couple of extra wires off the usb connection to power a small 60mm fan for cooling the cam. There seems to be a fair amount of heat on the Divio NW801 during operation so I may attach a small heatsink to this directly under the fan to aid cooling.
More to come soon.
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