TUESDAY, FEBRUARY 18, 2020
DIY Canon mirror control cable
I wanted to make my own cable for controlling the mirror of the Canon
40D DSLR while using the Backyard EOS software. This would allow still
photography with the camera viewfinder mirror locked up to eliminate
vibration. This is often an issue with astrophotography at fast exposures,
like planetary or double star imaging. Ultimately, made a cable based
on Paul Beskeen's circuit where he used an opto-coupler as I was attracted
to the isolation benefit and the status indicator feature. I thank
Guylain Rochon for his support.
N.B. Interconnect between DB 4 and 6 not shown!
technical info:
When using the Canon 40D DSLR camera on its own, one can command
the mirror to lock in the up position.
When using an external intervalometer, the option setting for the
mirror lock-up can be used in conjunction with the self-timer function.
But if one is using remote control software like Backyard EOS, it
is a little more complicated with the 40D body.
I built a custom cable to control the mirror in a Canon 40D, inspired
by the Beskeen design. I used an opto-coupler. Rather than sacrifice
an intervalometer, I found an adapter cable with the Canon N3 plug.
Needed the pin-outs for the N3 cable...
When I switched to the audio stereo 4 pole screw terminal connector
from Sayal, I needed to confirm the pin-outs.
The screw positions are marked:
- L - corresponds to the plug tip
- R - the middle ring of the plug
- nothing
- ground symbol - the sleeve or base of the plug
This custom cable assembly with the Neewer N3 adapter allows the
Backyard EOS software to lock the mirror up as needed.
- master power switch to avoid noise transfer
- discreet yellow and red LEDs for status indication
- electrical isolation between the camera and computer
- serial port DB-9 interface to computer
- proprietary N3 interface to camera
my custom wrap build costs:
- classic DB 9 serial plug, female, in parts bin - free, in a way
- yellow and red diffuse 5mm LEDs - free
- switch from parts bin - free
- resistors for LEDs - in parts bin, pennies
- opto-coupler or optoisolater 5 KV transistor, 4-DIP - 57 cents
ea.
(Digi-Key, DK # 160-1366-5-ND, bought 2, used 1)
- MOSFET, N-CH, 60V 200mA, TO-92 - 50 cents ea.
(Digi-Key DK # 2N7000FS-ND, bought 4, for testing - did not use)
- 10K resistor for testing, 14¢ - did not use
- Velleman sub-mini female stereo jack - $2.95
(Sayal, CD030, GAP 1423, 239418)
- Neewer Canon N3 adapter cable - $8
(Amazon Canada)
- printed circuit board, breadboard, perf board in parts bin
research and build time:
- research and testing: 6 hours
- build time: 6 hours
references:
lessons learned?
- The awkward documentation with Backyard EOS didn't help a lot
in understanding what exactly is going on in the software and with
the camera. A lot was inferred. Much was discovered in close observation.
- Using stranded wires turned out to be essential given the cable
assembly would need to be flexible and robust.
- Serial communication signals and voltages flip from positive to
negative and can vary by 12 to 15 volts!
- MOSFETs are field effect transistors and not unlike regular (bipolar)
transistors.
- First use of opto-isolator chips. Opto-couplers act like a switch.
Send in a signal, send in light, and the switch closes.
- Opto-couplers must be current limited in the input side (given
that they have an internal LED).
- I have considered cable requirements with a computer only having
USB ports. This custom cable uses serial communications and therefore
I might need 2 USB-serial convertors, say when I'm controlling a
mount while imaging...
things I might add or change:
- I have yet to place the circuitry bits in a proper protective
box.
- The yellow LED I chose is awfully bright. Perhaps, if I do this
again, I'll use an orange.
MONDAY, FEBRUARY 17, 2020
bits and bobs
Here I describe the parts for the camera mirror control build. Many
were accumulated over the years from various sources including A-1,
Sayal, The-Store-Formerly-Known-As-RadioShack, and Active Surplus.
- old Psion serial cable with female DB-9 connector, with all 9
leads, unshielded
- 470 and 330 ohm resistors, 1/4 or 1/8 watt
- low mcd, diffuse red LED (for exposure indication)
- low mcd, diffuse yellow LED (for standby indication)
- small SPST switch
- Lite-On LTV-817 opto-isolator transistor from digi-key, 4-DIP
package
- female 2.5mm submini audio stereo jack (with screw terminals),
from Sayal
- four conductor wire
- other cabling to make it all work
- Neewer Canon N3-to-2.5mm submini plug from Amazon
- breadboard, approx. 1.5cm x 2.0cm
Not strictly part of the build but you'll likely need to be away
from the camera or the computer so a serial 9-connector extension
cable, straight-through, is required.
Tools, equipment, software, etc. used. You can do your own thing
of course but this is what I used.
- computer resources
- Express SCH and PCB
- internet
- note-taking system, e.g. Evernote
- testing
- Maxitronix Electronic Lab with breadboard for prototyping
- digital multi-meter
- alligator jumper cables, for jumping
- 40D camera body
- Backyard EOS software
- Windows computer
- USB-serial adapter
- tools
- soldering iron, adjustable
- sponge
- helping hands
- close-up glasses
- side cutters
- wire strippers
- alligator jumper cables, for heatsinking
- small vice
- needlenose pliers
- sewing pin
- tiny screwdriver
- hacksaw
- breadboard
- logic probe
- supplies
- heat shrink tubing
- solder
- water
And I used a digital camera to photo-document things...
MONDAY, FEBRUARY 17, 2020
blog links
Scattered through the blog proper are detailed reports and updates
on the build with some posts showing photos. Reverse chronological
order.
- imaged SLE 235 without mirror locking, 21 Jul '17
- tested
the field, worked!, 27 Sep '16
- tested cable, got yellow
LED!, 19 Sep '16
- new
version of BYE to try, 17 Sep '16
- gave Guylain a "light
bulb", 17 Sep '16
- no luck with Force
mode, 15 Sep '16
- sent in test
results, 12 Sep '16
- Guylain suggested
Force option, 12 Sep '16
- redirected
to EOS support forum, 11 Sep '16
- interconnected
pins 4 and 6, 11 Sep '16
- noted the pin-outs of the Sayal submini jack, 11 Sep '16
- no success, did I have a bad
setting? , 10 Sep '16
- switched to stranded
wires, 9 Sep '16
- experienced mirror vibration while imaging
doubles, 4 Sep '16
- finished
mirror control cable, with couplers, 22 Jun '16
- switched to Beskeen circuit with opto-isolator, 20 Jun '16
- took more test shots with Covington design, 18 Jun '16
- updated BYE, Backyard EOS, 3.1.6 , 11 May '16
- got nervous,
3 May '16
- tested custom mirror cable again,
it worked!, 24 Apr '16
- verified two
cables needed, 24 Apr '16
- tried to control mirror, with
MOSFETs, 23 Apr '16
- received
Neewer cable , 15 Apr '16
- received
parts, including MOSFETs, arrived, 5 Apr '16
- ordered
MOSFETs and opto-couplers, 3 Apr '16
- used mirror control in trails
imaging , 1 Aug '15
- considered mirror cable, started research, 5 Jul '15
- made sequence
charts with mirror lock option, 28 Jun '15
- double star run, no mention of mirror lock , 15 Jul '15
- reviewed mirror
control with intervalometer, 26 Jun '15
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