Electronics: quick and cheap EQDIR

[pete_l]

A couple of nights ago my commercial EQ Direct USB-Serial to HEQ5 mount interface died.
Rather than spend £30 and wait for it to wing its way to Spain, I looked for a DIY solution - of which there are many.

However, they all specify that you must use a USB-Serial board that outputs 0 - 5V data to the mount. Since I mess around with arduinos, I have a lot of USB-Serial boards, but they all only supply 0 - 3.3v data and the mount doesn't respond.

A quick rummage through my junk-room (yeah, it started out as a junk box: 40+ years ago)  revealed some 4-way, bidirectional, level shifters from BitsBox. Essentially these take two supply voltages, tagged "low" and "high" voltage and convert signals from one regime to the other. In this case I used a CP2102 USB-serial board which has both 3.3v and 5v supplies. I connected the 5V to the "high" (HV) pin on the shifter and the 3.3v to the "low" (LV) pin. They share a common 0v that also goes out to the HEQ5.

After that it just required connecting the CP2102's RxD and TxD to the "LVx" pins of the shifter and snipping the cable off my defunct EQ Direct and connecting its wires to the corresponding HVx pins.  Amazingly, it worked!

Here are a couple of images to give an idea of what I built. The level shifters are part# M042 from bitsbox.co.uk. Less than £1 each and very reasonable P&P.

 

[wimvb]

Thanks for sharing. That will certainly come in handy at some point. Did you open the eqdir to find out the wiring (tx, rx, 0, Vcc), or is that obvious? (Haven't checked on my eqdir yet.)

[pete_l]

Yes, I opened it up for a post-mortem There were only three wires and the circuit board conveniently had the connections labelled. So all I had to do was attach the salvaged cable with the RJ45 connector to the same pins on the new USB-serial board.

[kroy]

are these EQDIR cables some special or can we just buy say one of these 

https://www.amazon.co.uk/s/ref=nb_sb_noss?url=search-alias%3Daps&field-keywords=usb+to+rj45+ftdi&sprefix=usb+to+rj%2Caps%2C147&crid=22HM5PFAGOAS0

 

[Dr_Ju_ju]

It would depend on the wiring of the RJ45, the voltage of the switching sinal 3v\5v etc. 

They are designed to be used with Cisco equipment, so even though they have an FTDI chip, they may well not work.