Adapting a TTL-232R-3v3 cable for an EQ8

[pmrid (Peter)]

Could one you electronic wunderkind please help me figure out which cable goes where - I've bought one of the 3.3 VDC TTL cables to use with my EQ8 with EQMOD. Bu I'm having trouble figuring out the cableing for the RJ45 (8P8C) plug. The data sheet lists the pinout for their 6-pin connector as:
1. GND - black
2. CTS# brown
3. VCC red
4. TXD orange
5 RXD yellow
6 RTS# green

The EQ8 manual gives the pinout for the hand controller (an 8-pin plug not 6) as:
1 and 4 GND
2 and 3 (no connection)
5 Tx
6 Rx
7 and 8 Vpp+

i just had a quick look at a Shoestring Astronomy USB2EQ5 cable and note that it uses 6 wires only with nothing in slots 7 and 8 whereas the Synscan hand controlled has wires in all 8 slots. Mystery deepens?


I'm a bit stumped.

Peter

[mswhin63 (Malcolm)]

Hi Peter,

You only need GND, VCC, TXD and RXD.

GND -> GND
VCC -> VPP
TXD -> RXD
RXD -> TXD

The Rx and Tx are usually the one that goes wrong, so if it doesn't communicate (recognised) the first time then swap the Rxd Txd.

CTS (Clear to Send) and RTS(Ready to Send) are not used in EQMOD.

[pmrid (Peter)]

Originally Posted by mswhin63

Hi Peter,

You only need GND, VCC, TXD and RXD.

GND -> GND
VCC -> VPP
TXD -> RXD
RXD -> TXD

The Rx and Tx are usually the one that goes wrong, so if it doesn't communicate (recognised) the first time then swap the Rxd Txd.

CTS (Clear to Send) and RTS(Ready to Send) are not used in EQMOD.

Thanks Malcolm.
I'm wondering now whether I actually need the VCC/VPP at all - the EQMOD documentation seems to suggest that only GND, RX and TX are needed.

http://eq-mod.sourceforge.net/tutindex.html - scroll down a bit to about mid-page where they talk about the FTDI cable.

Any thoughts?

Peter

[mswhin63 (Malcolm)]

The FTDI TTL module may require power from the source (being the EQ8) to provide the correct logic level. If you have a multimeter measure the VCC pin and VPP pin while powered to see if they both have a supply voltage usually 3.3V in your case. One usually does not read the voltage and is the reason for connecting both together.

But units must be referenced with the correct voltage although in most cases that is done by the GND connection.

[Tandum (Robin)]

I foresee a small cloud of smoke.

Is the thing you bought USB? if so it should be powered from the PC so you will only need RX, TX and Gnd going to the mount. That's 12v coming out of the mount socket, I doubt your device would like that.

[mswhin63 (Malcolm)]

I just checked my set-up and I use the VPP to power my Bluetooth module, The other connection are only RX TX and GND for the data.

As mentioned earlier measure voltages and if there is a voltage present on both VCC and VPP then connect only the GND, TXD and RXD

[chrisshillito]

Originally Posted by pmrid

Thanks Malcolm.
I'm wondering now whether I actually need the VCC/VPP at all - the EQMOD documentation seems to suggest that only GND, RX and TX are needed.

http://eq-mod.sourceforge.net/tutindex.html - scroll down a bit to about mid-page where they talk about the FTDI cable.

Any thoughts?

Peter

The instructions on the EQMOD Website are quite clear and tried and tested - they are all the advice you need.

There is 12V coming out of the mount and on some EQDIRECT types (Bluetooth, RS232) this is used to provide power. However, the ftdi USB cable takes its power from directly form the USB (5V) line so the only connections you have to make are GND, Rx, and Tx.

If you are fitting your own RJ45 plug then just omit the 12V line completely. If your are splicing a cable to your ftdi cable and the 12V line is present on the RJ45 then you should carefully isolate it.

Please be warned that if you manage to short the 12V line to either the Tx or Rx lines you will permanently damage both microcontrollers (one for each axis).

Chris.

[mswhin63 (Malcolm)]

EQMOD does not require minimum 4V, if that information is on the website then it is incorrect. The mount requires the correct logic conversion whether it is 1.8, 3.3 or 5V. (1.8V is experimental ATM)

EQ5 and 6 mounts require a minimum 4 V to make it work not the other way around.

I would check the specs properly on the EQ8 if it is 3.3V then many people have it connected wrong. It may work OK for a period of time but may fail very early voiding any warranty.

3.3V is also a high speed logic level so running at 5V will limit the speed of communications as well.

[pmrid (Peter)]

Originally Posted by mswhin63

EQMOD does not require minimum 4V, if that information is on the website then it is incorrect. The mount requires the correct logic conversion whether it is 1.8, 3.3 or 5V. (1.8V is experimental ATM)

EQ5 and 6 mounts require a minimum 4 V to make it work not the other way around.

I would check the specs properly on the EQ8 if it is 3.3V then many people have it connected wrong. It may work OK for a period of time but may fail very early voiding any warranty.

3.3V is also a high speed logic level so running at 5V will limit the speed of communications as well.

The schematic for the hand controller that appears in the EQ8 users manual shows both the TX and Rx lines as 3.3V so I assume that distinguishes it from the EQ5 and 6. I read somewhere that the interface is 5 volt-tolerant but is designed for 3.3.

Peter

[mswhin63 (Malcolm)]

Hi Peter, If the manual says that it is 5V tolerant then it is fine but if you already have 3.3V level FTDI then that will be better. The primary reason for lower voltage level is that it take less time to reach 3.3V then it takes to reach 5V, hence 3.3V can work faster. The technology to read logic 3.3V has only been achievable recently (10 years)

So it is better to run on the complaint voltage if only just to make sure.

EQ5 and 6 were made before 3.3V logic became mainstream so it wouldn't have been the best to change half way through production. This is good engineering practice. Anyway I hope managed to get as much out of this thread but it appears you only need to connect GND, TXD and RXD only.

[pmrid (Peter)]

Yep, thanks Chris, Malcolm, Robin. Appreciated.
Peter

[chrisshillito]

Originally Posted by mswhin63

EQMOD does not require minimum 4V, if that information is on the website then it is incorrect. The mount requires the correct logic conversion whether it is 1.8, 3.3 or 5V. (1.8V is experimental ATM)

EQ5 and 6 mounts require a minimum 4 V to make it work not the other way around.

The 4V limit comes in when considering the 5V interface of the EQ6 Pro and HEQ5. The USARTs of the mount controllers for these mount types have schmitt trigger Rx inputs and these require a level of 0.8xVcc to trigger. 0.8x5 = 4V and this is why those using 3.3V interface cables have found that they do not work with these mounts even though the normal switching threshold of 5V ttl might lead some folks to believe they would.

I would check the specs properly on the EQ8 if it is 3.3V then many people have it connected wrong. It may work OK for a period of time but may fail very early voiding any warranty.

Unlike the earlier mounts the EQ8 and AZ-EQ6GT have been designed with 3.3V signalling interface. However, this interface has been designed to be 5V tolerant in order to maintain compatibility with the synscan handcontrollers. This information comes from synta technical staff and was obtained by Richardo Contreras, the skywatcher dealer for Argentina and Chille who approached me when it became clear there was some confusion over the use of EQDIRs and EQ8s. This info was initially posted to the EQMOD yahoo group and re-posted in the EQ8 topic on this forum (by Robin).

So, there is no inherent danger in using an EQDIR using 5V logic levels with an EQ8 - that is what your handcontroller is doing anyway. 5V EQDIRECTS have been widely used with the AZ-EQ6GT mounts for quite some time now with no problems.

When it comes to warranties you really need to check with your dealer as you may find that some would argue that that plugging anything into it, other than the synscan, invalidates the warranty. If this concerns you, or you have any doubt you could always use PC-Direct mode during the warranty period.

3.3V is also a high speed logic level so running at 5V will limit the speed of communications as well.

The mount interface only runs at a fixed low speed (9600 bps), there is absolutely no limit imposed on actual mount communication speed when using 5v signalling compared to 3.3V

Chris.

[mswhin63 (Malcolm)]

Originally Posted by chrisshillito

The mount interface only runs at a fixed low speed (9600 bps), there is absolutely no limit imposed on actual mount communication speed when using 5v signalling compared to 3.3V

Chris.

Yeah I sort of worked that out after going to the auctions today, just got back to update. Speed is not going to make a real difference in this case. Skywatcher must have some practical engineers to even consider capability issues. Most I deal with try to phase out 5V logic now. Thumbsup for Skywatcher

Thanks Chris for making clear everything.

[coldknights (Cathy)]

So what do we now name this thread now( Adapting a TTL-232R-5v cable for a EQ8 ) ?

[chrisshillito]

Originally Posted by coldknights

So what do we now name this thread now( Adapting a TTL-232R-5v cable for a EQ8 ) ?

I can't see anything wrong with tread title. Those with an EQ8 or an AZ-EQ6Pro are in the lucky position of being able to use either a TTL-232R (5V) or TTL-232R (3.3V) cable for their EQDirect interfaces and this thread highlights that fact.

Chris.

[coldknights (Cathy)]

Good to see people can use both cables as you have described .

[RobF (Rob)]

Originally Posted by Tandum

I foresee a small cloud of smoke.

Is the thing you bought USB? if so it should be powered from the PC so you will only need RX, TX and Gnd going to the mount. That's 12v coming out of the mount socket, I doubt your device would like that.

Would like me to help wire it up?


This is a good thread for USB/TTL to RJ45 concoctions actually: USB EQDir for under £4

[coldknights (Cathy)]

Good link Rob thanks for sharing and it looks like a lot more people out this weekend with soldering irons making this cable.

[RobF (Rob)]

Just make sure you carefully check each wire with a multimeter at the end before wiring it up Cathy and you should be fine.

[pmrid (Peter)]

Originally Posted by RobF

Just make sure you carefully check each wire with a multimeter at the end before wiring it up Cathy and you should be fine.

I have done a rewire of one of these FTDI 3v3 cables and thought I might share what I have done. I have isolated the black, orange and yellow wires and cut the remainder short. The 3 wires I have then inserted in slots 4,5 and 6 of the RJ45 plug. These are supposed to be the Ground, TX and RX respectively - according to the FTDI spec sheet.

To be clear about this, I count the slots from left to right looking down on the RJ45 plug with the Tab underneath and with the plug facing forwards (i.e. the wires enter from the side closest to the viewer).

I have used installed the right drivers and connected the USB to my 64 Bit laptop. It recognized the device and established a COM port as expected.

I then used a multimeter to measure the voltages across the 3 wires using slot 4 (Ground) for the negative and measuring the other 2 I got readings of 2.96 and 3.36 volts respectively.

I don't know whey they are different. Perhaps someone else does.

Peter