DIY pedals/brake via Logitech DSUB

Hi everyone,

I did a quick google search but came up empty on this. Has anyone tried interfacing a DIY peripheral (handbrake, H-shifter, pedals) with the logitech G920 via its onboard DSUB connectors? Is the data coming out of these peripherals serial encoded (and if-so is there a proprietary handshake?) or is it just direct pin-outs of switches and pots? If it's the latter, then the 920 would be a great test bed for the operation/mechanics of DIY controls without having to fight with much in the way of electronics or embedded software.

Thanks in advance!

Hi @Gambledog. Its been a while since I used my Logitech g27 which I assume is the same internals as the G920 but ill give you what help I can.
The pedal set is just 3 10k potentiometers directly connected to the wheel base via the dsub connector. You could directly connect to that socket if you wanted to build a diy set of pedals but id be sure to continue to use 10k potentiometers so the current draw from the wheel base is the same as stock. The downsides to those pedals are that they are only 8bit resolution (256 potentiometer steps) when plugged into the wheel base and they don't have a load cell brake pedal which in my opinion is a must for any serious sim racer. As for the H shifter gear lever and handbrake mods that you mentioned they are just connected to buttons as standard so would be relatively easy to mod both. However there is a better and much better way to do what you mentioned.
The better way would be to plug the pedals directly into your pc using a bodnar cable you would get 10bit resolution (1024 potentiometer steps) on each pedal. This improves brake accelerator control x4.
http://www.leobodnar.com/shop/index.php?main_page=product_info&cPath=97&products_id=187
The much better way is to buy a leo bodnar interface which is only £3.00 more than the cable and wire the pedals to that
http://www.leobodnar.com/shop/index.php?main_page=product_info&cPath=94&products_id=183
The controller is a serious bit of kit. I use this very model on my tilton 600 pedals, paddle shifters and button box on my rig. The controller has 12bit resolution (4096 potentiometer steps) on all analog inputs and a dedicated loadcell input also at 12bit resolution so you could wire your pedals to the inputs as they are then upgrade to a load cell later. You can also connect 36 buttons or 16 rotary encoders or a mixture of both in a matrix with a 8 way hat switch and all usb plug and play.
You could build a diy hand brake using a potentiometer instead of a button and be analog like the pedals. You would probably have to gear the potentiometer for more rotational travel but the more you pull the lever the more e brake you will get in the game rather than the on/off that a button gives which the G920 base will be limited too.
You could build a button box using momentary switches/buttons, rotary encoders and wire it to the controller. Wiring is fairly simple and Encoder software is free from the leo bodnar website.
A diy H shifter I would just plug into the wheel base as there is no benefit using up buttons on the bodnar controller (buttons are buttons wherever there connected too).
I don't think you would need to upgrade this controller in the future as its that good and a very major upgrade to any sim as it will do 3 pedals, handbrake, paddle shifters and button box easy with no code to write. Just download DI view software from the bodnar website for setup and calibration.
A Ricomotech loadcell upgrade for the brake pedal is a good mod from stock. The pedal is really firm with almost no pedal travel at all but is better than the stock brake pedal
https://www.ricmotech.com/Load_Cell_Upgrade_Kit_for_Logitech_Pedals_p/rmt-lc27.htm
Hope this helps
Matt

This is definitely helpful. Thanks! I think the LB board will be the way to go for PC controls. I didn't realize the 920 pedals were only 8-bit resolution.

I found a diagram for the shifter that shows x/y data for the shifter on 2 pins (pots presumably) but there are serial in and out pins for button info and dead links to arduino scripts that talked it through a calibration/handshake. Unlike the pedal it seems like it's got some proprietary communication going on. The detailed documentation is lost to a time when modders were still paying attention to the G25/27.

Since I want to keep playing while I build my PC/VR/Motion setup I'm hoping to keep console compatibility early-on which is the only advantage to talking directly to the g920 base unit.

Build thread for the 2DOF will start as soon as I get my cordless angle grinder and take a trip to the scrapyard.

I didn't realize you wanted to keep console compatibility as you didn't mention it in your first post. I just assumed you were a pc sim racer looking to build a motion rig or some of the other great stuff fellow sim racers on this website have built.
I don't have a Logitech wheel set anymore as I gave it to a fellow sim racer years ago when I got my direct drive wheel and to be honest I never tried to mod the shifter as I never used it. I built a button box for the pc, unplugged the shifter completely and just used the paddle shifters. I cant test any of this for you but ill try to help assuming the G920 is just a g25/g27 in a new dress
Ok it seems you were right about the shifter, it does indeed use 2 potentiometers for gear stick position and 2 shift registers for the buttons daisy chained and using spi to communicate with the wheel base. The wipers on the 2 potentiometers are wired directly to the Dsub connector and are basically used as analogue buttons.
give this a read.
http://forum.arcadecontrols.com/index.php?topic=134988.0
The black / red buttons, hat switch and reverse switch all wire to shift registers (74hc165d or similar as the ones suggested in the schematic are no longer manufactured) and are wired like this

You will probably have to check and change the pin configuration of the Dsub connector as Logitech seem to change this model to model.
If you want to add a e brake then I suggest u try this

hope this helps

This helps! I think I'll keep it simple and just do the sequential shift, pedals and handbrakes as console-compatible mods. If/when I do the H shifter I'll probably go straight to something USB compatible.

The goal of this mini-project is to sucessfully design/machine something small, attainable and non weightbearing before I start on the frame for a motion rig. Going console-compatible means I can limit the electronics to simple soldering (rather than also adding a microcontroller project to the mix).

I'm learning to do a bunch of stuff I've only casually read about before, so I'm trying to break it down into one new skill at a time with some tangible endpoints early on to keep me motivated.

Again, thanks for tracking down the diagrams!