Archive for September 2014

Converting the Suncom SFS Throttle to USB

The time has come to convert the Suncom throttle as well.


Suncom SFS Throttle


The Suncom SFS is a pretty well made throttle with split grip and programmable buttons. The programmable feature was good for the days where game ports could only support 4 buttons, but USB game controllers have no such limit.

I strongly recommend reading the previous post on the Suncom joystick as it has several tips I will not repeat here.


Suncom SFS hardware overview

The Suncom SFS have pretty dense electronics under the hood. It has 3 separate PCBs and a whole bunch of cable harnesses. As opposed to the Suncom joystick, there is no separate controller for the buttons. Instead, the buttons are electronically ordered in a grid of 4 by 4, and need to be scanned sequentially to get their status.


Suncom SFS original electronics


Preparation before fitting the new hardware

1. Remove the old PCBs

3 PCBs need to be removed. The first one is the smallest. It holds the 2 extension connectors. Remove the screws and pull the PCB out. You will probably need to use some force and bend the surrounding plastic to get this one out. Do it carefully. The other 2 PCBs will be easier to remove. When removing the mid size PCB, pay attention that this will loosen up the 4 red button cups, take care not to loose them.


Throttle’s 3 PCBs taken apart

2. Disconnect cables.

The main body should be disconnected now from the PCBs. There are 2 cable harnesses coming from the grips (11 pin and 5 pin) and 4 wires coming from the potentiometers.  All the wires are connected to the main PCB. The cables should be just pulled out from the board. The 4 POT wires should be de-soldered.


Disconnecting cables and wires


3. Adding a 3rd wire to the POTs

In the original electronics, as in all PC Game-Port devices, only 2 wires are connected to the potentiometers. But in our case we need 3: VCC, GND and return. So, as in the joystick case, we need to add another wire to the POT’s pin number 3. The POTs are not easily accessible  for soldering. To get access we need to detach the grip assembly from the main body.  To do that, first remove the 4 screws attaching the grip assembly to the body:


Yes, this time the screws are not just for decoration

Now carefully lift the grip assembly out of the main body. You will need to play with it a bit and again maybe use some slight force to do it. Be very careful not to damage the wires while doing so!

Now that the POTs are accessible, add a 3rd wire to both POTs by soldering an extra wire to pin number 1 (might be pin no 3 if the POT is flipped)


Right pot, a wire should be soldered to pin 1


Left pot with pin 1 already wired

Note wire colors for later:  Wire connected to the pin closest to the front of the throttle (pin 3 on both POTs in my case) is the VCC. Back wire is the GND, and middle wire is the return.

You can now reattach the grips assembly back to the body, again, careful on the wires.

 4. Salvaging parts from the main PCB.

Some electronic components from the main PCB are needed for reuse. You will need to carefully de-solder the following parts: The 9 LEDs, the 4 tact switches, the slide switch, the 5 pin connector, the 22 pin right-angled pin header, and the 4 diodes.


Components from main board needed for the new PCB

Preparations done!


Assembling the new PCB

1. Collect necessary parts

Order a PCB from Itead Studio, using the attached Gerber Files.
Order parts from digikey or another place, using the attached BOM.
Find a USB cable.  I used a USB2 extension cable, and just cut the female end.
(For any of you who wish to play with the PCB, here is the complete KiCad project: SuncomSFS_Kicad)

2. Assemble the PCB

Start with the SMD parts.As noted in the Joystick post, there are many Youtube tutorials on how to solder smd parts. Here is my method:

For resistors/capacitors, First apply some lead with the soldering iron on one of the pads on the PCB. Then using tweezers pick the resistor/capacitor and solder one side to the already coated pad. Now that the component is fixed into place go ahead and solder the other side.

For fine pitch ICs, such the PIC MCU, again, apply some lead on one of the component pads on the PCB, then solder the component to its place, and since only 1 pin is being soldered to the one coated pad, it is easy to play with the IC until all pins are aligned correctly. Then solder another pin on the other side of the IC fixing it into place. Make sure that all the pins are still aligned to the pads, and then start to solder all the rest of the pins. You don’t have to be accurate and it is OK if you short a pin or 2 at this stage. When all pins are soldered, Use solder-wick to remove excess lead from the pins, freeing any of the shorted ones on the way. Use a cleaning solvent to remove any leftover dirt. Using a magnifier glass  inspect and make sure all pins are soldered correctly and no shorts left.


New PCB with smd parts assembled

Next, Solder all through-hole components (3 connectors, 5 switches, 4 diodes and 9 LEDs). For each components, first solder 1 pin, then make sure the component is places correctly, and only then solder the rest of the pins. (if it is not places correctly, since only one pin is soldered, you can heat-up this pin with the soldering Iron and move the component until it is placed correctly.) for the LEDs, pay attention for the polarity: align the strait cut on the bottom of the led dome with the strait line on the PCB symbol. The LEDs should have a small bending on their leads helping you place them at the correct height above the PCB. Note also the diodes polarity – black stripe on diode goes to the white line on the PCB.
Important note: The the JST programming connector goes on the BACK side of the PCB.

3. prepare the USB cable.

To hold the new cable nicely into the body, we need to reuse the rubber gasket that held the original cables. There are 2 cables passing through the gasket. Cut both cables as close as possible to the surface of the gasket from both sides.


Cable gasket. Cut on both sides.

After cutting the cables, pull out all internal wires from the gasket to free the holes. Take the new USB cable. If you use a USB extension cable as I did, cut out the female side. Try to pass the cut edge of the new cable through the gasket hole (either of them).  If the hole is too tight, measure the cable diameter, and use a standard drill bit with the similar diameter to widen the hole. Make sure you insert the cable from the correct side.


New USB cable inserted through gasket.

After the cable is inserted, expose about 1 Inch of wires from the cut edge, then from each wire expose a few millimeters of copper.

It is very important now to make sure the wire colors of the USB cable are correct. (In my case I found out that they ware not). Using a multimeter or similar device make sure the wire colors are as in the following pinout table:


USB type A connector looking from the front side.

1. Red (VCC)
2. White (D-)
3. Green (D+)
4. Black (GND)

If the wiring is not correct, make sure you map them correctly when connecting to the PCB.

4. Connecting the PCB to the main body

First you want to solder the USB cable to the PCB. Use the following image to see where each wire goes:


USB cable to PCB wire connection.

Now you need to connect the 3 x 2 potentiometers wires.  Solder the POT wires using the image below and the notes you made at step 3 of preparation stage.


Left POT connections


Right POT connections

Last, you need to connect the 5 and 11 wire cables coming from the grip assembly. There is only one way to connect the 5 pin connector. The 11 pin connector connect to the upper line of pins in the 11 pin header, noting that the side with brown and black wires are toward pin number 1.


PCB fully assembled and connected to main body.

 5. Fitting the PCB in place.

Before placing the PCB in place, make sure the slide switch is aligned with its cup on the body. Now carefully place back the 4 red tact switch caps. Make sure the springs in the cups are placed correctly. Carefully turn the PCB upside down making sure all connected wires are getting in the way of the switches or the screw holes. Screw back the 3 PCB screws to hold the PCB in place.


PCB fit in place.

That’s about it for the hardware part!

Programming the software

The software for the PIC is similar to the one used on the F15 joystick. Similarly, when the slide-switch is on (LED is lit), several buttons become toggle buttons. The left and right grip are mapped to X and Y analog axis. In addition there are 16 switches, and 2 8-direction POVs.

Download the project from this link: SuncomUsbThrottle_PIC18F25K20

Use the same procedure as in the Suncom Joystick post to program the Throttle.

That’s it for the software part!

Final touch

Before closing everything, 2 last things should be done:

1. You may want to cover the original extension connector holes by inserting back the small connector PCB. Cut all wires coming out of it before you do so.

2. As one of the readers suggested, place a cable tie at the entry side of the USB cable, to make sure the cable will not be accidentally pulled out.  (Thank you, Craig!)


Final touch


Cable entry and extension connectors in place

Thats all!

Close up the bottom plate, and enjoy your renewed Suncom SFS Throttle!


As asked by Rajeen, here is a (rough) button connections diagram for the grip: GripButtonDiagram