USB EQDir for under £4

[12dstring]

Take one PL-2303 USB-serial cable (e.g. USB to UART (TTL) Cable module PL2303 Converter | eBay) - £2.99

One 2m RJ45 ethernet cable (e.g. 2m BLACK RJ45 CAT5 PATCH ETHERNET NETWORK CABLE LEAD | eBay) - £0.99

Remove one end of the ethernet cable and strip back, check wiring colours.

The USB serial converter has a small circuit inside:

As a side note, the little PCBs are great for mods that need a serial interface such as webcam long exposure mods or DSLR shutter cables. The DTR and RTS signals required for them are indicated below (labeled A and B on the PCB). Note the chip is a 3.3v part with 5v tolerant inputs, so make sure you choose a part to interface it with which as Ok with 3.3v level signals (i.e. 74LS00 for the SC1 mod). Ideal for compact USB-only mods as done by yesyes ( http://stargazerslounge.com/diy-astronomer/148315-spc900-lxmod-yesyes-style.html), the chip is the same type, but the PCB smaller as it doesn't have the RS232 voltage level converter meaning you can interface directly with logic levels parts instead of needing diodes+transistors.

(You don't need to worry about RTS and DTR for the EQDir.)

Connect the two cables as follows:

Gnd-Gnd

Rx-Tx

Tx-Rx

If your connector wiring colours are exactly the same as in these pictures, then the connections are as follows:

Black - Orange/white + Solid blue

Green - Blue/white

White - Solid green

Pair the unused solid brown + brown/white off together (12v)and insulate them from the others. Same with the solid orange and green/white.

Do check with a multimeter before hand to make sure you have the 12v lines correctly identified.

Make sure all lines are nicely insulated and give it a test, and add some heatshrink when done.

Worked first time on my XP laptop. Will try on Windows 7 64 bit later.

Total cable length is a little under 3m, can be extended 5m on the USB side.

This is for the HEQ5, for the EQ6 just swap the RJ45 ethernet side with an RS232 DB9 cable and use the EQ6 pinout here: http://eq-mod.sourceforge.net/eqdirect_232.png

Edited January 11, 2012 by 12dstring

[beamish]

DAve,

firstly, nice to see you posting again , feels like you've not been around ,here or UKAI for a while and secondly, -superb and just what I was thinking about getting

[Gina]

Brilliant! Thank you I might even replace my HitecAstro EQDIR box with a nice short made up cable like that and save some mess on my mount.

[Reggie]

Nice find Dave, I was looking at some usb to serial boards on ebay (ego china ebay shop) for a similar purpose, yours are a bit cheaper than those

[malc-c]

Dave, did you cut open the converter or does it bolt together ?

Also is it 5v TTL or 3.3v ??

I'm in need of making a new canon shutter release, and this might fit the bill

Should of read the post a bit closer

Edited January 11, 2012 by malc-c

[Reggie]

It's 3.3v with a 5v tolerant input for the RX pin from the original post. I haven't looked at the chip involved but I'm guessing that the chip takes 5v in from the usb, then has an onboard regulator for 3.3v, and the IO pins are configurable for 3.3v/5v depending on whether the vccio pin is tied to 3.3v or 5v, at least that's the way it works on an ftdi cable.

Edited January 11, 2012 by Reggie

[12dstring]

I know I've been quiet for a while, finishing my degree and now living the dream working as an observatory technician now. It's no excuse for not posting more though...

I was aiming for a neat all-USB approach for my setup. One USB cable to my SPC900NC guider, and my DSLR is going to be modified to include a USB hub with an 'auxilary port' on the side of the camera box. The EQDir can then plug into the camera and I'll only need 2 USB cables going between the camera and mount (plus power).

Dave, did you cut open the converter or does it bolt together ?

Also is it 5v TTL or 3.3v ??

I'm in need of making a new canon shutter release, and this might fit the bill

The converter casing can be pulled apart with the aid of a thin flatheaded screwdriver, and can be pushed securely back together again.

To clarify, the chip in the converter is a 3.3v part, but the Rx input is 5v tolerant (so no problems talking to the mount). All the outputs from the converter will be at 3.3v. I'm planning to use one for my Canon DSLR shutter control using NPN mosfets (which trigger at 1.5v), but the normal transistors will work just fine.

Edit: The chip is a PL-2303HX (rev. A). Here's the datasheet if you want more details: http://www.prolific.com.tw/support/files/%5CIO%20Cable%5CPL-2303HX%5CDocuments%5CDatasheet%5Cds_pl2303HX_v1.6.pdf

Edit 2: No problems running Win7 64 bit

Edited January 11, 2012 by 12dstring

[Starjumper]

Hi Dave,

Nice find and nice to see you back posting.

John

[malc-c]

Dave, thanks for the info. I've just ordered a few to have a play with. Beats the £17 I paid for the last cable. The good news about splitting the case means that wit care it might be possible to fit one or two additional components in the case. I'm looking at using a 4N25 opto isolator directly connected between the PCB and the camera for a serial shutter release for my 400D - I've tested it on the breadboard, now hopefully will be able to produce a neat end product at the end.

With regards to the cable length, traditionally serial cable has longer runs before a repeater is required. Not sure if that applies to these new TTL levels, but if it similar, then extending the cable on the serial side may be better than on the USB side.

One other option is to crimp an RJ plug on the end of the cable and secure with a small amount of glue...assuming the stock cable length these adapters come in is OK for your set up

[Reggie]

Thanks for clearing that up dave, I wasn't sure if it was a standard 3.3v with 5v tolerant inputs or whether you could actually change it to be 5v IO. It seems that you either get 3.3v or 2.5v, so I was completely wrong and should've known better than to assume that they might have similar features to an ftdi chip.

[chrisshillito]

To clarify, the chip in the converter is a 3.3v part, but the Rx input is 5v tolerant (so no problems talking to the mount). All the outputs from the converter will be at 3.3v.

So is the Tx output to the mount just 3.3V? The PIC USART in the mount is expecting 5V. Whilst 3.3v may be enough to switch ttl please consider that the comms protocol being used has absolutely no error detection / correction capability to handle a marginal comms environment.

Chris.

[Reggie]

While we're on the question of pic usart, is it anything like avr usart where different clock speeds will give different error margins at different baud rates chris?

[FrankieValley]

Thanks for the post. I shall be making one up for my EQ6. Always good to have a bit of a tidy up and I can replace my old EQDir 'box' that is velcroed to my mount. Also, the only thumb screw on the EQDir RS232 connector snapped and I'm reliant on friction to stop the plug falling out. That is stress I can do without

[FrankieValley]

So is the Tx output to the mount just 3.3V? The PIC USART in the mount is expecting 5V. Whilst 3.3v may be enough to switch ttl please consider that the comms protocol being used has absolutely no error detection / correction capability to handle a marginal comms environment.

Chris.

Hi Chris,

Glad you posted. Are you nervous that this may not work 100%? This is taken from your site and I know you are familiar with it - Please be aware that FTDI produce a similar product, the TTL232R3V3, but due to lower signaling voltages this will not work

[12dstring]

I originally planned to have a little 3.3v-5v level shifter circuit as well, but I left it out after I tried without and it worked. I've had mine running over the past month with no issues.

I'll open up my mount tomorrow and check the specs for the PIC, if it would prefer more than 3.3v then there's enough room inside the converter to add a few components to bump up the output to 5v.

[chrisshillito]

The PIC will most likely take anything over over 2V as being a "high" signal and anything lower than 0.8V as being "low". The "problem is that in lowering your max level down to 3.3V you don't get the same immunity to noise/interference and voltage drop over cabling etc. we are after all taking the TTL lines "off board" in this application. If its working fine for you then great - I do think however it would be good idea to provide folks with the details of how they might bump up the signal levels to replicate the functionality of the existing EQDirect designs (even if they opt not to do it).

Chris.

[chrisshillito]

Hi Chris,

Glad you posted. Are you nervous that this may not work 100%? This is taken from your site and I know you are familiar with it - Please be aware that FTDI produce a similar product, the TTL232R3V3, but due to lower signaling voltages this will not work

I'm just nervous that it may not work as well, all the time, in all applications (and I'll end up with more "comms error" related support ). The 5V design replicates what the synscan does so we can be confident that we're operating within the design spec of the mount interface.

Chris.

[12dstring]

It's a sound point.

The simplest method is probably the mosfet+2 resistors as shown here: Bi-Directional Level Shifter – HUSSTECH

The 2N7000 is a TO-92 part so should fit in the case snugly, and the two unconnected pads along the bottom next to Tx are 3.3v and 5v if I remember correctly so should be easy to tap into them.

I've only got surface mount mosfets at the moment, which I know isn't everyone's cup of tea, so I've ordered a few 2N7000s and will post back with pictures when they arrive.

Another way to help with any noise issues is to shorten the cable, and extend if needed on the USB side. If you need more than 5 metres then probably best to stick with the RS232 version.

Edited January 11, 2012 by 12dstring

[Reggie]

I'm ok personally, I've got the 5v ftdi cable, a 5v/3.3v sparkfun ftdi breakout board, a barebones ssop 28 breakout board with ft232rl chip on it (also 3.3v or 5v IO) and one of these DLP Design USB Product Page (it does jtag as well) and another 3x ft232rl ssop chips ready to go into projects

[yesyes]

With regards to the cable length, traditionally serial cable has longer runs before a repeater is required. Not sure if that applies to these new TTL levels...

No. The advantage of the RS232 levels serial port was that they used + and - 9 to 15Volt. It is the direction of the current that determines whether a specific bit is high or low. The actual amount of voltage and current is not so important. Therefore voltage drop over longer cable runs is much less of an issue.

This is not true for TTL levels. If the voltage drops below the safe high level of the receiving device, communication becomes unstable. With 3.3V instead of 5V outputs the max cable length reduces quite a bit. Safe high levels of 5V TTL devices are usually around 2.5V. So you can't afford to lose a lot.

[Gina]

I think the confusion arises from the term TTL (Transistor-Transistor Logic) which used 0v and 3.3v as low and high logic levels. As I recall the average actual switching level was about 1.8v. Whilst TTL chips are still available they have generally been replaced by CMOS (Complementary Metal Oxide semiconductor) logic which has different specs. Although these devices still run on 5v (though they can run on higher voltages) the locic levels are 0v and 5v with the average switching level around 2.5v as I recall. Being not very different from TTL logic levels people tend to use the term TTL.

CMOS logic levels are 0v and Vcc (the supply voltage) with half that as the switching level generally. I like to run CMOS logic at 12v to give greater noise margins but if these mounts use 5v supply then you're stuck with a lower noise margin and using 3.3v rather than 5v makes things even worse.

[Glider]

I have tried both 3V and 5V types and can say that the with 10m of cable at the RJ45 mount end the 3V didn't work but the 5V did.

10m gets from my conservatory to the patio.

[12dstring]

Recommended mod to bring the signal output up to 5v

Either of these circuits will do, to help with noise immunity and longer cable lengths.

My implementation:

Top

And fitted back in the case:

Edited January 12, 2012 by 12dstring

[FrankieValley]

Thanks Dave.

[beamish]

umm, bottom line is will Dave's original work ok for 3m or less of cable ? I don't wish to start adding transistors or owt else to it once it arrives cos I don't know what I'm doing- it needs to be a "dummies" version for some of us