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EQDirect Bluetooth build, using logic level converter?

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#1 Russky

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Posted 19 July 2019 - 04:41 PM

Hi all,

 

I’m just getting into astrophotography and have purchased my first Goto mount, the HEQ5. I’m wanting to hook everything up with a Raspberry Pi, using Astroberry for a start. I’ve ordered all the part off eBay to build both an EQDirect USB cable, and an EQDirect Bluetooth connector, based on the schematics on the EQMod website.

 

After ordering all the components for the Bluetooth build, I realised that in MOSFETs & Resistors are basically logic level shifting, and there are single board logic level shifters that can do that for you these days.

 

Is there any reason you can’t replace those components with the single boards? I know the boards require power on both the 3.3v and 5v side, which is combined doing it the schematic way,  but it would save a bunch of breadboard wiring and soldering going that way instead of building the pcb myself?

 

Any thoughts on the build process from those who have done it themselves would also be appreciated.

 

Thanks. Russell.



#2 steveastrouk

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Posted 19 July 2019 - 08:02 PM

I built a BT to mount connection with one cheap regulator, a 9 pin D connector and a BT module. I think there were around 6 wires ? Or am I missing something?



#3 Russky

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Posted 19 July 2019 - 08:34 PM

I built a BT to mount connection with one cheap regulator, a 9 pin D connector and a BT module. I think there were around 6 wires ? Or am I missing something?

Oh I couldn't find any 5V logic level modules at a decent price, so I've ordered the 3.3V ones, so as a result, there needs to be a logic level shift between the input and output signals. I've seen some people say it works without it, but I don't want to risk any connectivity issues, so I'd like to do the proper logic level shifting.

 

Russell.



#4 steveastrouk

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Posted 20 July 2019 - 10:07 PM

IIRC, the inputs to the BT from the mount are 5V tolerant, and the outputs are sufficient to drive the mount 's 5v inputs.



#5 Russky

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Posted 20 July 2019 - 11:49 PM

Really? I could see the BT Rx possibly accepting 5V, but everything I’ve seen on the mount says it needs at least 4V to trigger a high signal. Unless the output tolerances on the HC-06 aren’t that great, so the 3.3v is driven higher, depending on the input voltage? Bad design if it is, but would work to make things simpler. Guess I’ll just have to see when the parts arrive. My biggest concern is blowing up the mount, but we’re talking about lower voltage on the Rx input, so hopefully that won’t be an issue.


Edited by Russky, 20 July 2019 - 11:50 PM.


#6 phonehome

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Posted 21 July 2019 - 01:17 AM

Why not use them.  I take it you have you looked at the bi-directional 3.3 to 5v logic level convertors/shifters?  I know Amazon has 100's of them in various configurations, # of channels, etc.  

 

Example:  https://www.amazon.c...aps,180&sr=8-19

 

Certainly a lot easier, less expensive and more compact than bread-boarding it.

 

Ed


Edited by phonehome, 21 July 2019 - 01:26 AM.


#7 Arjan

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Posted 21 July 2019 - 02:25 AM

In my experience, with a HC06 you have to shift levels.

#8 Russky

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Posted 21 July 2019 - 02:25 AM

These are the ones I’ve ordered https://rover.ebay.c...tm/191950926334

 

Looking at the circuit diagram they’ve provided, it looks pretty much the same as the EQDirect wiring diagram on the EQMOD web page, just split into two different sources. 

 

*EDIT*

 

Wait, actually I’m not sure it does? The Tx line is being shifted either way, but maybe the Rx signal is only being down shifted from 5v to 3.3v coming from the scope, but I can’t see where it’s being pulled up to 5V going into the scope? Unless I’m reading it wrong (and I’m only a tinkerer, not an expert at electronics) I may need to keep looking....

 

*EDIT #2*

 

Oh wait, i think the converter I/O naming is confusing me. I don’t even need to use the Rx channels on the converter, do I? There’s two Tx channels, so I just connect one for the BT Tx to scope Rx, and the other for the scope Tx to the BT Rx, it just that the output aide 9n the converter is called Tx HV, but that’s the signals going to the Rx ports on the module and mount. 


Edited by Russky, 21 July 2019 - 03:12 AM.



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