Update readme

README.md

@@ -1,2 +1,33 @@
 # sanwa_opt
-Optical sensor mod for Sanwa buttons (such as Pop'n Music, SDVX or IIDX)
+Optical sensor mod for Sanwa buttons (such as Pop'n Music, SDVX or IIDX)  
+<img src="docs/img1.jpg" width="50%">  <img src="docs/img2.jpg" width="50%">  
+<img src="docs/img3.jpg" width="50%">
+
+Traditional Sanwa buttons used in arcade use micro switches which wear out through time.
+This project creates a optical sensor module that can replace the whole original lamp/switch holder and the microswitch. It almost never wears out.
+
+I build it originally for my Pop'n Music controller, the Sanwa OBSA-100UMP button. And it turned out Sanwa has its own standard and my design works for many other Sanwa buttons such as SDVX and IIDX.
+
+## PCB
+The PCB contains the optical sensor part and the LED lamp part, you need to cut the lamp part from the main board.
+
+For the optical sensor, the PCB supports both ITR1203 (small) and the ITR8402 (big) but I would only suggest to use the ITR1203, small and perfect.
+
+* R1 is the current limiter for the emitter, 1206, 500ohm to 1K is fine.
+* R2 is for pulling down the out level, 1206 or 0805, 10K is fine.
+* R3 is the current limiter for the LED lamp, depending on the brightness of the LED, 1206, 50ohm to 200ohm is fine.
+* For the LED, choose 2835 or 3528 3V high brightness LEDs.
+
+## Holder
+You need to print out the holder.stl. A resin printer is perfect for this. I'm not sure if an FDM printer with PLA has enough accuracy to do the work.
+
+## Installation
+1. Solder the lamp part onto the main board.
+2. Use M1.8*8 screws to fix the board onto the holder.
+3. Remove old lamp/switch holder from the button.
+4. Push this new optical sensor back into the button.
+
+## Sorry for the ZHR-5 interface
+The interface to the mainboard is a ZHR-5, which is compatible with Sanwa's own buttons with optical sensors. I haven't made other types of interfaces yet. Maybe I will in the future.
+
+* Good Luck! *