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jansonntag:attempt3
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jansonntag:attempt3 [2021/02/07 18:10] 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 178: | Line 181: | ||
| - In the loop, I just read out the value of coil 0 (key D) and store the value in an array | - 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 | - 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/attempt3.1612721459.txt.gz · Last modified: 2021/02/07 18:10 by jan
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