Opto Isolator?

[A320Flyer]

Guys,

I have made the SimpleGPUsb described in this thread: http://stargazerslounge.com/diy-astronomer/81238-simplegpusb-home-brew-auto-guider.html

and it works great.

The only thing is that, when I connect my AC Power Adaptor to my Canon 1000d it creates interference in the Simple GpUsb which then sends erroneous guiding commands to my mount.

I have read about Opto Isolators and I wondered if this would solve this issue and if it would be possible to add one to the SimpleGpUsb circuit or build one that fitted in-line on the USB lead or the power lead.

Any guidance would be very welcome.

Thanks

Bill

[malc-c]

Bill, I can't really answer your question, but I don't think you could add one to a USB lead. Opto Isolators can be thought of as (in loose terms) like a relay. They isolate one side of a circuit from another, typically is a switching type circuit, but unlike a relay they can't drive a high current directly.

Looking at the circuit it's just a basic RS232 TTL to USB converter with a set of darlington drivers (which appeared to have buffered outputs) that simulate the button pushes on the syntrek handset. Problem could be that the 232 /USB brakeout board is the wrong type. They do two versions, 3.3v and 5v TTL, and its the latter that would probably work better (at least that's what I use for my EQDIRECT cable for the EQ5 and HEQ5 mounts). The one thing I would do is ground all the un-used inputs to the darlington array....

One possibility is that it's the AC adapter used for powering the canon camera that's causing the problem... is that a commercial product or something you've built yourself ?

Other than that I'm at a loss... but hope that helps

[A320Flyer]

Malcolm,

Thanks for your response. I'm not sure if it was the 3.3V or 5V board that I bought but it was this one

CP2103 USB to Serial Board from Cool Components

I made 2 of the SimpleGpUsb units and both give me the same problem. The AC Adaptor is a generic one I bought from ebay.

I suppose I could try grounding the unused pins as you suggest. There are some unused ones on each side of the Darlington Array. Do I connect ALL of these to the common ground?

Cheers

Bill

[malc-c]

The give-away is the pin out description on the breakout board (assuming it's the one in your link) as it has 3.3v out. This voltage is too low. If you look at the board schematic VDO is 3.3v and that is connected to the VDD input, so the chip and all TTL logic levels will be 3.3v. http://www.sparkfun.com/datasheets/PCB/CP2103%20Breakout-Schematic.pdf

I've used these before SparkFun Breakout Board for FT232RL USB to Serial (BOB-00718) | Proto-PIC.co.uk which have a jumper that is unsoldered to give 5v TTL levels, however it doesn't have the general purpose i/o's. The way I would mod the CCT is to replace that darlington array with a general purpose transistor, and switch the 5V from the USB line via the transistors - totally untested, and would need breadboarding... but could work

[malc-c]

Or simply connect one of these in the circuit. Could try it before the darlington if not after

Logic Level Converter - SparkFun Electronics

http://www.sparkfun.com/datasheets/BreakoutBoards/Level-Converter-v10.pdf

[A320Flyer]

Hi Malcolm,

I've ordered a couple of the Logic Level Convertors. Can you tell me how it is connected? Do you have a diagram of any sort? Electronics is not my strong point - not even close!

Cheers

Bill

[malc-c]

Bill,

I've never used one, just stumbled on it when browsing the sparkfun web site.

According to the image below, you would simply connect the 3.3v GPIO 1 output to TX1 of channel 1 and then the the wire that went to GPIO1 to TX0 and then repeat for channel 2. You would thus need two of those logic shifters to connect all 4 GPIO's

Hopefully this will resolve the issue and the syntrex will then register the 5v TTL pulses in the same way as it would if you had pressed the buttons.

EDIT, further reading still requires 3.3v and GND from the USB/232 board, and then you need 5v and GND on the HV side.... Hummmmm... to be honest I'm not 100% sure it will work as the GND from the syntrek and the USB ground are not common and the sysntrek is running at 6v (?) which might upset the voltage divider side of the board. Hopefully someone with more electronics experience could jump in here and advise as I wouldn't want you to fry your mount

[Reggie]

Actually, the sparkfun 0718 ft232rl breakout does have gpio (it's a function of the chip) we mostly use it in it's serial port mode though (although cts/rts/dtr are used as if they were gpio for things like the spc900nc long exposure mods).

It entirely depends how you use your breakout board Check the datasheet and the ftdi website for more details, it's as well featured as the cp2103 chips.

Other uses for the ftdi breakout are as a programmer for AVR/arduino chips (google avrdude), this is incredibly hand as you can build and program your own arduino style boards from scratch.

[malc-c]

Further reading for you.

Sensor Interfacing - SparkFun Electronics

Most of these devices are used to allow 3.3v chips to interface with PICs and other micro's that use 5v TTL levels. If the syntrek mount uses 6v I personally don't think that would make much difference as we're not using the level shifter in bi-directional format. If the syntrek is running at 12v then that might be an issue.

You will also need to do some experimentation (which is the fun of electronics) in that the level shifters might work better before the darlington array, as the darlington might have a higher current tolerances than the mosfet on the level shifter

On the subject of experimenting, this was my last electronics project

It's a microchip based 4 channel pulse proportional thermostat controller with dual channel light switch for heating and lighting reptile enclosures. This was the development board...and yes I did blow up the odd component when I miss-wired something on the breadboard

Took almost 9 month of development to get to the prototype shown above... but it's been worth it...

[malc-c]

Actually, the sparkfun 0718 ft232rl breakout does have gpio (it's a function of the chip) we mostly use it in it's serial port mode though (although cts/rts/dtr are used as if they were gpio for things like the spc900nc long exposure mods).

On checking the datasheet http://www.sparkfun.com/datasheets/IC/FT232R_v104.pdf CBUS pins 0 to 3 can be configured as GPIO pins, but this has to be configured first by "programming" the EEPROM using a utility from the FTDI website (FTDI Utilities) the user guide for this app can be found here http://www.ftdichip.com/Support/Utilities/MProg.pdf

Bill it seems we've dragged up a lot of bed time reading for you

[Reggie]

ftdi do lots of interesting multipurpose 232/ttl/245 chips, there's one they do thats about £20 that does jtag, it also does dual uart but the board I've got doesn't break the 2nd uart pins out

[A320Flyer]

Malcolm/Reggie,

Thank you both for your input but I'm afraid that all of what you have explained is so far over my head that I cant even see it never mind understand it. I suppose I was hping for a quick fixit, a sort of "solder one of those in there" type of fix, but that obviously isnt going to happen.

Thanks again.

Bill