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    Since I had some questions via private message: ...

    Since I had some questions via private message: the basic idea is to start a hardware timer, wait till runs out and then run NOPs for the remaining time. The timer is too granular to use it alone.
  2. I'd use differential pairs running to pseudo...

    I'd use differential pairs running to pseudo differential ADC inputs as much as possible.

    I'd use a 10 ohm series resistor and a 10u cap (vs .1u) on +5V to the op amp.

    Maybe just a resistor...
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    For the record, here is an improved crystal...

    For the record, here is an improved crystal layout. Note that it has a full guard ring that is only grounded at a single point. But Paul was right, crystal issues were a distraction. The real...
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    The charging circuit (uses a TI bq24092) is...

    The charging circuit (uses a TI bq24092) is missing the output decoupling capacitor.
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    So the PCB in question has a USB port and uses 5V...

    So the PCB in question has a USB port and uses 5V from the USB to power a lithium battery charger IC. And the CPU runs from this (typically around 4V). Every voltage checks out perfectly with a...
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    Can anyone confirm that pin 26 is 4V tolerant? ...

    Can anyone confirm that pin 26 is 4V tolerant? I have a weak pull up to the voltage of a lithium battery. I think the datasheet is trying to say that all pins except 9,10,11,12 are 5.5V...
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    Lifting pin 26 on several bad boards didn't fix...

    Lifting pin 26 on several bad boards didn't fix them.
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    Now that I understand how critical pin 26...

    Now that I understand how critical pin 26 (~EZP_CS/PTA4) is to the first boot process, I'll check for soldering/board errors that could ground it. Maybe even the gate capacitance of a mosfet makes...
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    All good advice, thanks everyone. Eventually...

    All good advice, thanks everyone. Eventually this will get fixed and I'll report the results.

    I populated a board with just MK20, decoupling caps and MKL04 and it worked - but maybe just because...
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    I haven't been able to get a good board to fail...

    I haven't been able to get a good board to fail to load. I could try to mildly heat/cool the board and crystal, hoping to make it fail.
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    I've been reviewing the Kinetis K20 manual...

    I've been reviewing the Kinetis K20 manual section 6.3.4 (boot sequence). I see that I am using pin 26 (~EZP_CS/PTA4) and that I have a 130K pull-up resistor and a small mosfet gate connected to...
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    I checked and I'm getting reset pulses every...

    I checked and I'm getting reset pulses every 15-18 usec. This is much less than 50-56 usec, but I don't what this means. Evidently something is going wrong earlier in the startup process.
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    Evidently standard behavior on a unprogrammed...

    Evidently standard behavior on a unprogrammed MK20 is to produce brief pulses on the RESET line every 50-56 usec. If you see longer than that, then the system is getting further along. If RESET...
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    Here is the section with the crystal layout. I...

    Here is the section with the crystal layout. I know, not the best, but the same layout worked reliably on a previous board. There is a continuous ground plane immediately under this top layer. ...
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    It seems like I could have two cases: a) the...

    It seems like I could have two cases:

    a) the MKL04 loads code into the MK20 that activates the crystal and then the crystal fails and the MK20 resets

    b) the MKL04 never gets to the point...
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    Custom board using MKL04 - yield problems

    I've built a custom "teensy" board that uses the MKL04 chip. Problem is that only 1/3 of 20 boards are working (ie programming with Paul's bootloader code and then showing up as a USB device) -...
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    Have you done it?

    Have you done it?
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    Alex: sorry, it's not clear to me. You tested...

    Alex: sorry, it's not clear to me. You tested your code on the 3.5 and 3.6 and it works now? Line 2 of the code suggests otherwise.
  19. The routine does flush the cache, which will...

    The routine does flush the cache, which will temporarily slow down the execution of other code. But I can't see any reason that it would cause a permanent slow down.

    Try commenting out the...
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    See here for some discussion of 3.5/3.6 changes....

    See here for some discussion of 3.5/3.6 changes.

    https://forum.pjrc.com/threads/43165-Over-the-Air-firmware-updates-changes-for-flashing-Teensy-3-5-amp-3-6

    If you have untested code, please...
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    That would be great. Would be really nice to get...

    That would be great. Would be really nice to get the Teensy 3.5 and 3.6 modifications into it too.
  22. I agree with others - use serial. On the other...

    I agree with others - use serial. On the other hand, shared SPI or I2C ram would be interesting.
  23. The AD8675 can handle 18 V, so 15 V has...

    The AD8675 can handle 18 V, so 15 V has adequate margin. IMO, you need to be just as cautious with 10V as 30V.

    If you need more than ~12 bits, I'd use an external ADC.
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    IMO, every serious developer should learn to use...

    IMO, every serious developer should learn to use a debugger - it really does fix bugs faster. On the other hand, print() and pin outputs are more universal/generic and eventually work.
  25. Say that the op amp or ADC used has -56db of...

    Say that the op amp or ADC used has -56db of PSRR. As I see it, that means you can have -40db of power supply ripple and still be fine with a 16 bit ADC. I expect that you can achieve this without...
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    If speed isn't an issue, then setting 16 bits and...

    If speed isn't an issue, then setting 16 bits and oversampling/averaging is helpful.
  27. Might be worth it to try using this one. Compare...

    Might be worth it to try using this one. Compare the results to two 9V batteries.
    ...
  28. You can add a series resistor and large capacitor...

    You can add a series resistor and large capacitor to ground to filter the 3.3V before it is applied to R2.
  29. Lots of capacitance helps PS noise. And keep...

    Lots of capacitance helps PS noise. And keep switching power supply switching speeds far above your frequency of interest (so that ripple is easily filtered out). This is worth reading. ...
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    As others have said, wherever possible, resistors...

    As others have said, wherever possible, resistors on outputs help prevent accidents.
  31. I had good results (about 15 bits with an...

    I had good results (about 15 bits with an external 16 bit converter) using that design wizard. Probably not immediately obvious is that amplifying to a high (12-20V) voltage and then reducing it...
  32. Let's say you want to measure 1-200 lux and have...

    Let's say you want to measure 1-200 lux and have .1% resolution, even at 1 lux. That normally requires 17.6 bit, 100 Ksps ADC, which you aren't going to achieve. Adjusting aperture on a lens will...
  33. I would use a differential input ADC, a low pass...

    I would use a differential input ADC, a low pass filter and as much oversampling as possible.
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    I confirmed that a 2K pullup to 5V on a digital...

    I confirmed that a 2K pullup to 5V on a digital pin set as an input or a low output caused no apparent damage to a teensy 3.1. So I saved a transistor in the case of a teensy switching 5V with a...
  35. Nice work. The original code has "FMC_PFB0CR |=...

    Nice work. The original code has "FMC_PFB0CR |= 0xF << 20; // flush cache", but I'm not surprised that 3.5/3.6 needed different/additional command(s) to accomplish this.

    Hopefully someone can...
  36. Thread: Z-Wave

    by jonr
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    Also consider the $25 ACC-UZB2-U USB dongle from...

    Also consider the $25 ACC-UZB2-U USB dongle from Digikey plus some code from OpenZWave.
  37. switch statement - case using string/char array

    Despite being useful, it's correctly thought that you can't do this:

    char s[100];
    // input s here
    switch (s) {
    case "test1":
    ...
    case "test2":
    ...
    }
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    OK, I updated the first post with a new URL.

    OK, I updated the first post with a new URL.
  39. I've used both relay boards and SSRs and I prefer...

    I've used both relay boards and SSRs and I prefer the latter. The teensy can drive it directly.
  40. The teensy loader is best, but if you really need...

    The teensy loader is best, but if you really need to the update firmware via the serial port, the "flasher" code here is simple to use and works well.
    ...
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    If you want to upload hex files to a teensy via a...

    If you want to upload hex files to a teensy via a serial port, the "flasher" code here works well.

    https://github.com/Photosynq/PhotosynQ-Firmware/tree/master/multispeq1
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    > 16 bits of ADC performance is likely only...

    > 16 bits of ADC performance is likely only achievable on a external ADC.

    And even then it can be hard to get. Lots of ways that noise can get added.
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    I received my device and it works quite well.

    I received my device and it works quite well.
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    I've done all the different options and when I...

    I've done all the different options and when I have a choice, I still use the teensy loader.
  45. Thread: Teensy Express

    by jonr
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    Maybe add a few Grove connectors too.

    Maybe add a few Grove connectors too.
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    More oversampling usually helps with the number...

    More oversampling usually helps with the number of bits from the ADC. Also disconnect the USB.
  47. As an aside, specs are better and I've had good...

    As an aside, specs are better and I've had good experience with the BME280.
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    > a simple pinMode(disable) I'd like to see...

    > a simple pinMode(disable)

    I'd like to see this implemented.
  49. The above ideas sound best, but for some...

    The above ideas sound best, but for some applications you may want to consider updates over serial port or bluetooth using your own PC software.

    See the "flasher" code in...
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    > the caps are 100nF in 0402 Best to use the...

    > the caps are 100nF in 0402

    Best to use the largest, reasonably priced value in the package size you choose (perhaps 1uF with 0402). The beneficial effect of this shows up clearly in tests.
    ...
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