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The Best I/O Scanner Solutions for Remote control
When designing a custom remote control product, we often use more buttons. But the I/O resources are tight, one or two I/O ports will be available if we save those ports in other modules. Unfortunately, it is still not enough. One more IC will be added to scan the keys. Although each IC is not expensive, it is a huge expense for remote control manufacturers who produce in large quantities and have low-profit margins, like DUSUN.
So, is there a better way to scan the keys? For example, with the fewest I/O ports, sweeping the most keys? The answer is yes. How many keys can be scanned if there are 5 I/O ports? Please see the following options, which is fully practiced by China leading remote control designer and manufacturer DUSUN.
Option 1: Matrix Scan
The schematic design drawing of matrix scan method as shown in picture 1. Total 5 input/output ports, 3 of them are used for row scan and 2 I/O for column detection. Specifically, the row line is used to output the scan key code, and the column line will detect whether there is a key query method to scan it. The process is as follow: In the row line, the 011, 101, and 110 scan key values are sequentially output. When each row line outputs a scan key value, the column line will detect at once. When the column line detects that there is a button, the corresponding button can be judged by the combined scan key value. So if matrix scan method used for remote control design, each 5 I/O ports could only scan 6 keys in total.
Picture 1: Matrix Scan Schematic Drawing Sample
Option 2: Matrix Scan + Ground Extension
The schematic design drawing of Matrix Scan + Ground Extension method as shown in picture 2. The process is as follow: First, detecting 3 row I/O ports and scanning K1', K2', K3'. Then performing 2*3 sweeping process according to Option 1 method. In this situation, 5 I/O ports can sweep 9 keys.
Picture 2: Matrix Scan + Ground Extension Schematic Drawing Sample
Option 3: Trapezoidal Scan
Picture 3 shows the schematic design for method of Trapezoidal Scan . The process is as follow: Set first I/O1 value as 0 and detecting I/O2-I/O5. If there is a press of corresponding key, it works. Otherwise, the scan will continue. Setting I/O2 output to 0 and detecting I/O3-I/O5. We will see whether there is a key press, and so on. Note: When scanning an I/O port (output is 0), the swept ones should not be detected. For example, setting the IO2 output to 0, and detecting I/O3-I/O5 in turn. There is no need to detect I/O1, otherwise an error will occur. In this case, the 5 I/O ports could scan 10 keys in total.
Picture 3: Trapezoidal Scan Method Schematic Drawing Sample
Option 4: Trapezoidal Scan + Diode Expansion
A really fantastic key-scan solution for remote control design ! The unidirectional continuity of the diode is used to distinguish two symmetric keys. The idea is as follow: Scanning the keys one by one while the other four I/O ports can detect the corresponding four keys. In this way, the error in option 3 has been optimized. And with this solution, 16 keys could be scanned in total.
Picture 4: Trapezoidal Scan + Diode Expansion Schematic Drawing Sample
Option 5: Trapezoidal Scan + Diode Expansion + Ground Extension
25 keys can be swept out by 5 I/O ports, which is the ultimate best scanner solution for remote control. The process is as follow: Sweeping the 5 ground keys then scanning the rest keys following Option 4. If there is no button, scanning the I/O port button one by one. When a key is swiped to an I/O port, if there is a ground button pressed, it may be misjudged because the ground key has a higher response priority than the other keys. For example: when sweeping I/O1 and the output is "0", the K62 is pressed. It is hard for I/O2 to recognize whether is K11 or K62. This misjudgment can be avoided in the program: when detecting the button, I/O2 will decide whether the ground button is pressed. If not, it should be K11. It is a realizable option for remote control manufactures.
To sum up, take key numbers as S. If the diode is enabled, S = (N-1) *N + N. If not, S = (N-1) *N /2 + N.
Picture 5: Trapezoidal Scan + Diode Expansion + Ground Extension Schematic Drawing Sample
About DUSUN ELECTRON LTD.
More than 16+ years of designing, developing and manufacturing, Dusun has been created and delivered billions of high-quality and cost-effective remote control devices worldwide. Our innovative remote control solutions designed based on a broad wireless technology portfolio, like BLE, RF4CE, 2.4G, IR and interactive paradigms: Air-mouse, Voice, Touch, Motion, Pointing and Virtual Reality control. Customers came from a wide range of industries, such as pay TV, PC/OTT, home automation, automobile, consumer electronics, IOT and so on. We always try our best to bring customers with value-added and different design experiences for their essential products and brand. Learn more