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jansonntag:attempt3 [2021/02/07 11:06] jan |
jansonntag:attempt3 [2021/03/24 17:10] (current) jan |
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| - | ====== Analog Cherry Keyboard Attempt 3 (WIP) ====== | + | ====== Analog Cherry Keyboard Attempt 3 ====== |
| After a while of looking at it, this seems far too complicated! There have to be simpler, cheaper, and more accurate solutions. I started searching for some ICs that maybe can do the trick but didn't found any good other than the links I posted above. But then Henrik found something great: The LDC1314 | After a while of looking at it, this seems far too complicated! There have to be simpler, cheaper, and more accurate solutions. I started searching for some ICs that maybe can do the trick but didn't found any good other than the links I posted above. But then Henrik found something great: The LDC1314 | ||
| Line 18: | Line 18: | ||
| I found even more detailed pictures on the website of the " | I found even more detailed pictures on the website of the " | ||
| - | + | They are only mentioning copyright for 2018 and 2019. The company seems to be very inactive. | |
| - | {{https:// | + | |
| Now with a 5V to 3.3V converter with ultra-low noise output. With all these bypass capacitors this has to be a super-duper ultra-low noise circuit. | Now with a 5V to 3.3V converter with ultra-low noise output. With all these bypass capacitors this has to be a super-duper ultra-low noise circuit. | ||
| Line 47: | Line 46: | ||
| So I need a 33.3kOhm resistor in front of the LTC6900 Set-Pin. | So I need a 33.3kOhm resistor in front of the LTC6900 Set-Pin. | ||
| + | <WRAP center round tip 60%> | ||
| + | This (the LTC stuff above) will get " | ||
| + | </ | ||
| + | |||
| And here is my first " | And here is my first " | ||
| Line 114: | Line 117: | ||
| Let's go through this code step by step: | Let's go through this code step by step: | ||
| - Import the library and the Wire library (I2C) | - Import the library and the Wire library (I2C) | ||
| - | - Then instantiate an LDC131X Object (the false means now alternative address) | + | - Then instantiate an LDC131X Object (the false means no alternative address) |
| - The lastTen and pointer variables are needed later to calculate an average of 10 measurements | - The lastTen and pointer variables are needed later to calculate an average of 10 measurements | ||
| - The setup starts with initiating the Wire and Serial communication | - The setup starts with initiating the Wire and Serial communication | ||
| Line 130: | Line 133: | ||
| - fREF0 = 43 Mhz | - fREF0 = 43 Mhz | ||
| - fSENSOR0 = 5960,977 kHz ~ 6 Mhz (See the Webench screenshot) | - fSENSOR0 = 5960,977 kHz ~ 6 Mhz (See the Webench screenshot) | ||
| - | - {{https://www4b.wolframalpha.com/ | + | - {{:projects: |
| - 8.9563 + Margin = 15 | - 8.9563 + Margin = 15 | ||
| - ldc1314.LDC_setClockDividers(0, | - ldc1314.LDC_setClockDividers(0, | ||
| Line 141: | Line 144: | ||
| - 40Mhz > 4 x 6Mhz -> reference Divider can be set to 1 | - 40Mhz > 4 x 6Mhz -> reference Divider can be set to 1 | ||
| - these two combine to 0x1002 | - these two combine to 0x1002 | ||
| - | - look up page 21 of the documentation two see the register map for CLOCK_DIVIDERS0 | + | - lookup |
| + | - ldc1314.LDC_setErrorConfig(0x0000) | ||
| + | - ERROR_CONFIG | ||
| + | - default | ||
| + | - ldc1314.LDC_setDriveCurrent(0, | ||
| + | - DRIVE_CURRENT0 | ||
| + | - I got the IDRIVE0 value from the table on page 40 of the documentation | ||
| + | - The best-fitting values (Nominal Sensor Current (μA), Minimum Sensor RP (kΩ), Maximum Sensor RP (kΩ)) where IDRIVEx Register Field Value 29 (b11101) | ||
| + | - INIT_DRIVE0 got set to 0 | ||
| + | - combined 1110100000000000 -> 0xE800 | ||
| + | - ldc1314.LDC_setMUXConfig(0x20D) | ||
| + | - MUX_CONFIG | ||
| + | - 0x20D -> 0000001000001101 | ||
| + | - Auto-Scan Mode Enable -> 0 -> Continuous conversion on the single channel selected (0) (just testing with channel 0 right now) | ||
| + | - Auto-Scan Sequence Configuration -> 00 -> Ch0 + Ch1 | ||
| + | - Input Deglitch Filter Bandwidth -> 101 -> 10 MHz (ƒSENSOR = 6 MHz) | ||
| + | - ldc1314.LDC_setGain(3) | ||
| + | - RESET_DEV | ||
| + | - 3 -> 16x gain -> 4 bits shift | ||
| + | - MOST IMPORTANT OPTION together with OFFSET. More about that later. | ||
| + | - ldc1314.LDC_setOffset(0, | ||
| + | - OFFSET0 | ||
| + | - 0x4FFF -> 100111111111111 (I know it's very high but that's needed) | ||
| + | - ldc1314.LDC_setConfig(0x0801) | ||
| + | - CONFIG | ||
| + | - 0x0801 -> 0000100000000001 | ||
| + | - Active Channel Selection -> 00 -> Perform continuous conversions on Channel 0 | ||
| + | - Sleep Mode Enable -> 0 -> Device is active (This is important to set after configuring everything. Otherwise the device will stay in sleep mode.) | ||
| + | - Sensor RP Override Enable -> 0 -> Override off | ||
| + | - Sensor Activation Mode Selection -> 1 -> Low Power Activation Mode (made no difference for me right now) | ||
| + | - Automatic Sensor Amplitude Correction Disable -> 0 -> Automatic Amplitude correction enabled | ||
| + | - Select Reference Frequency Source -> 0 -> internal oscillator (More about this later) | ||
| + | - INTB Disable -> 0 | ||
| + | - High Current Sensor Drive -> 0 -> 1.5mA max per Channel | ||
| + | - After configuring all the settings the LDC is now active | ||
| + | - In the loop, I just read out the value of coil 0 (key D) and store the value in an array | ||
| + | - If I have ten readouts I calculate the average and print it on Serial | ||
| + | |||
| + | As I found out through trial and error, because of the fact that the coils are so tiny and the spring inside the switch isn't huge either, I needed a high gain and a high offset. An easy way to describe this is like using a magnifier and looking at a specific part of the value. But if you want to find out more about this topic, this document here really helped me: [[https:// | ||
| + | |||
| + | As you may have seen I set the LDC to not use the external oscillator I put on the PCB. This is because I miss understood the reason for this pin to exist. It´s an alternative to the internal oscillator. I thought I would have to put in the value I calculated for ƒSENSOR in Webench. That's why I have a 6Mhz input now. This is not needed! The LDC will compare the oscillating frequency that comes back from the coil (this is the 6MHz I calculated) with the internal oscillator (40 MHz) or a given external oscillator. But the oscillating frequency should be greater than 4 x 6MHz. Because this isn't the case with the one I got, I´m just using the internal one. This works so the external one does not have to be populated on the PCB. This also saves in cost on the final PCB. I hope this was understandable. | ||
| + | |||
| + | Here you can see both the board and the plotter in action (recorded separately): | ||
| + | {{: | ||
| + | |||
| + | As you may see the graph shows when the button is pressed and how far it is pressed. But the result is not very accurate and there is a lot of interference. This is because of the high gain I set. But otherwise, there wouldn' | ||
| + | |||
| + | So there will be an attempt 4. There I will test out the bigger brother of the LDC1314: The LDC1614. It has the same pinout and overall package, so it will be an in-place replacement. The big advantage is the 28-bit resolution. Hopefully, there is no gain needed then. | ||
| + | |||
| + | \\ | ||
| + | [[JanSonntag: | ||
jansonntag/attempt3.1612695996.txt.gz · Last modified: 2021/02/07 11:06 by jan
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