Teensy 3.2 End Of Life

So sorry to see T3.2 go, it has been, and still is, great.
But i fully understand it has to go.
 
Not such a big deal, @Paul Thanks for all the efforts on the chip, I really learned a huge amount.
I too have been hit hard by NXP not getting all sorts of MCU's that I use.
Not entirely sure what their problem is, if it is some sort of effort to kill the entire lower end line.
Either way it is a shame, because in a lot of circumstances, the lower end MCU is all you need, e.g. battery life, price, etc.
Even so, I have my own bootloader not halfkay, but, that doesn't matter.
 
xxxajk said:
Not such a big deal, @Paul Thanks for all the efforts on the chip, I really learned a huge amount.
I too have been hit hard by NXP not getting all sorts of MCU's that I use.
Not entirely sure what their problem is, if it is some sort of effort to kill the entire lower end line.
Either way it is a shame, because in a lot of circumstances, the lower end MCU is all you need, e.g. battery life, price, etc.
Even so, I have my own bootloader not halfkay, but, that doesn't matter.
Click to expand...
I'm not going to speculate, but I'm sure profit has everything to do with its obsolescence, and I think the real loss was the LC as the 4.0 is the same price and way more powerful. On a positive note, how's the 4.1 replacement project for OC going, and will we ever see anything like the LC ever again?
 
I suspect during the chip shortage they prioritized the chips that were required by major industries like car makers and white-goods, no big mystery really.
 
MarkT said:
I suspect during the chip shortage they prioritized the chips that were required by major industries like car makers and white-goods, no big mystery really.
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I've been actively tracking the whole thing for a couple of years now.
It's pretty much exactly like the capacitor famine, which, we are actually at the tail end of.

You can blame a couple of things for the whole mess, which are very similar to the capacitor famine.
  1. Of course, the big guys like nvidia and amd got dibs on anything, which eat tons of silicon wafers, and those aren't exactly quickly produced.
  2. Then you have the fact that the node that they are on is getting more and more obsolete, so fabs tend to reduce the machines for that, and in place of those, install the newer process node machines.
  3. On top of all of that, any huge volume customers get preference, since it is a guaranteed sale.
There are a lot of other factors, but those are the main three, pretty much the same deal as the capacitor market famine.
 
Mouser even has 15K+ pieces on stock.
I would buy Teensy 3.2 if they are available - I have actually never needed the processing power of the T4 [and the related power consumption].

Paul
 
There are various posts where people would buy lots of T3.2 instead of moving their designs to T4.0.
Financially, there is a small risk that when T3.2 would be available again, everybody already moved to T4.0.

A better idea would be to design a small pcb, same size than T4.0, to minimize the pinout difference between T3.2 and T4.0. (mainly in the bottom side).
It will be inserted between the T4.0 and the T3.2 PCB. It will redirect the T4.0 pins to T3.2 pinout to allow minimal software changes.

Angelo
 
Teensy 3.2 is not coming back.

Angelo's comment about the financial risk is spot-on, exact for the "small" part. A word like "certain" or "inevitable" would be better.

Just to explain clearly, Teensy 3.2 was already a mature product when the chip shortages hit in mid-2021 and Teensy 3.2 stock ran out by January 2022. Had NXP delivered our orders on time in 2022 (most were already past the 52 week lead time by January 2022, the rest were late by June 2022), or even had they delivered more substantial quantity many months late, we probably could have kept Teensy 3.2 going for several more years. It is the normal life cycle of a tech product under normal circumstance of continuously supply, where "mature" gradually turns into "long tail" as customers with established applications continue buying for many years.

But that's not how things went. NXP delivered pathetic quantities only sporadically from late-2022 throughout all of 2023. Robin and I put a *lot* of work into allocation. Eventually that work turned into direct assistance to help customers migrate to Teensy 4.0, which freed up more of the extremely limited chip supply for those who hadn't migrated, and for occasional retail sale with low quantity limits (we really do care about helping makers). In hindsight, we probably should have put that work into Teensy 4.0 development and just discontinued Teensy 3.2 about 1 year earlier than we did. But that's with the benefit of hindsight. Throughout 2022 and 2023 people at NXP kept promising improvements which didn't come until 2024, which was far too late.

By mid-2023, most customers who had been using Teensy 3.2 in significant volume have moved on to Teensy 4.0 or their own custom PCB using the T3 bootloader chip or (sadly) other non-Teensy products. Several customers buying less regularly usually at lower volume were left, and some pretty widely used open source projects like Ornament & Crime were still tightly tied to the Teensy 3.2 hardware, but the long-term commercial damage to Teensy 3.2 was irreversible by early-2023.

I know this is hard to hear. I poured many years of work in Teensy 3.2 (and 3.1 & 3.0 which is evolved from), so believe me I know the pain! It was the first Arduino ecosystem microcontroller to support large non-blocking addressable LED projects in early 2013, and then DMA-based audio in 2015. I truly am sad to see Teensy 3.x go. It was as still is (would be) good on a technical level.

But PJRC is a small company which can't afford to make large financial mistakes, especially at a time when we're still recovering from having gone all-in to keep Teensy 4.0 & 4.1 (mostly) available during the shortages. The sad reality is Teensy 3.2 could have had many more years of "long tail" product lifecycle, had its life not been cut short at the "mature" phase by 2 years of shortages. The simple reality is nearly all customers who probably would have continued buying (in volume needed to keep Teensy 3.2 a viable product) for years to come were forced to move on during those 18 months. I know many people still want small quantities, and even some would probably use it in modest volume, but it's nowhere near enough bring back an already-mature product that has lost virtually all of its sustaining customer base.

Teensy 3.2 is absolutely not coming back.
 
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I didn't checked if they are already available anywhere, but PJRC could maybe provide production files (gerber, silk, placement, BOM,...).
Maybe by removing reference to PJRC for "PJRC would not be responsible for any damage....."
JLCpcb or PCBmain could produce some batches at low cost. But obviously not tested.

Angelo
 
Note the pinout for I2S is different between Teensy 3.x and Teensy 4.x. If you use the Teensy audio adapter, you need to get the version D or D2 board instead of A-C for the Teensy 4.0/4.1. Note, there are 2 I2S streams on the Teensy 4.x.
 
@PaulStoffregen
PaulStoffregen said:
Several times I've considered making an ADC shield. Might still do it. Recently have been playing with a relatively cheap (~$4) single channel 16 bit ADC chip and a 8:1 mux, both controlled with FlexIO. Input setting time is a difficult problem which leads to channel crosstalk, so not a simple thing, especially if running at speeds like 300-500 ksamples/sec. Of course there are chips with the mux built in, but the cost goes up quickly.

I hope you can understand with the built-in ADC, we simply have to live with whatever NXP provides. I really wish they would have done better. They probably do too, since they could sell more chips. But it's not so simple. Generally speaking, the improvements in silicon which allow digital circuits to run faster tend to make analog circuit less precise. With the much older & slower silicon used by Teensy 3.2, they were able to make the ADC better because the transistors were different, and specially certain analog circuits like a differential pair amplifier can be more precisely made than in chips meant for faster digital circuitry.
Click to expand...

First, aside, Paul have you tried that ADC we talked about somet time ago? That one has a mux and can share one opamp for all of the channels. I will post or send you the design files if anyone is interested, with the proviso that it is work in progress, I wanted to make another pass over package sizes and layout. Admittedly it might not be $4 all counted, but it seems pretty good.

Also, aside, I will be posting a really good analog input, maybe in the next few days, with a custom InAmp front end and high precision differential ADC. It connects by SPI.

Okay, now to the bit about why the analog inputs on microcontrollers are the way they are. I put a lot of time into investigating this recently. It is pretty interesting, in some ways. So far I have not found an exception to the following.

(Paul - is there any way to repost this to its own topic? I think it could be of general interest. But read on, I leave it to your wisdon. Please do let me know what you think.)

A lot of what goes on in the internal analog inputs seems to be driven by a few factors; space (including the size of the sampling capacitor vs sampling noise), cost on silicon, single ended supply and market (who it is designed for).

a) Space on the chip and the size of the sampling capacitor versus precision

Noise in any sampling input is limited by the sampling capacitor, according to the famouse kT/C ("kay tee over sea") noise,

v >= sqrt( k T / C)

where kT at room temperature is about 25 meV. Multiply C by 6.2E18 e/coulomb, and you see you have units of volts, i.e. sqrt(V^2).

Now, let's say we want 16 bits on a 3.3V input, about 50uV. The sampling capacitor noise needs to be smaller than that, so lets say about 8 to 10pf at a minimum.

How about 12 bits? Then we need noise small compared to 0.8mV and noise for a 1pf capacitor 60uV.

The size of an internal cap is real estate in a chip. That is one reason 12 bits is common, and 16 bits less so.

In fact, as it turns out, the K20 16 bit inputs, have 8pf to 10pf sampling capacitors and the 12 bit inputs have 4pf to 5pf


b) Kickback

The analog input almost always involves a switched sampling capacitor. When the switch closes to connecft the capacitor to the input, current has to be supplied by the source, to charge the capacitor to the required precision of the input voltage.
This has two important consequences

i) The carge draws by the sampling capacitor becomes a current. The current spike works out to be a voltage spike of V/R where R is the impedance of whatever comes in front of the capacitor, including your source impedance for the thing you want to measure.

ii) The sampling capacitor needs time to reach the voltage of your input,

V_cap / V_input = 1 - exp(-t/RC).

That means that to get to the precision you need for n bits, you need a sampling time > nbits x ln(2) x RC

For a 10 pf capacitor, and 50 ohm source, we need t > nbits x 0.7 x 10 pf x 50 ohm = 6 nsecs. Not bad.

iii) But, faster sampling, lower source impedance, means more current draw, more kickbacl.

In the above example, 10pf cap, 16 bits, we might need to supply 3V/50 = 60mA.

You might say, well I need to drive the ADC with an opamp. But that is still a lot of current for many opamps.

So the way it is usually done, is to put an RC between the opamp and the sampling capacitor. Now the C in the RC acts as charge reservoir and the opamp only need supply a smaller current to replenish the charge reservoir.

Here is what it looks like if you only use an opamp. See the large spikes when the switch S1 closes.

SAR_opamp_R100_cropped.jpg



And here is what it looks like with an RC between the opamp and sampling input. Now the red is current through C2, the cap in the RC in front of the input. Notice the current comes from that capacitor instead of being drawn as kick back through the opamp (or whatever else you might have attached if you were trying to use the analog input as a direct input).

SAR_opamp_RC20x1_currents_cropped.jpg




iii) Cost and market

The above with the RC, is the right way to do it. But to do that you need a negative supply for the opamp. You also need an opamp.

Here is what manufacturers choose to do instead. Honest to goodness, this is from the K20 datasheet (the Teensy 3.2.

Notice the resistor Radin in front of the ADC SAR engine (the sampling cap is inside the SAR).


K20-adcinput.png




Radin is 2K. So the current drawn by the sampling capacitor cannot be larger than about 1.6mA.

But now we need a longer sampling window, t > 16bits x 0.7 x 10 pf x 2 kohm = 220 nsecs. That still fits the sampling speed for the Teensy.

And by the way, this is why they tell you anyway, not to use a large source impedance. If you put another large resistor in front then you might need to be careful about the length of your sampling window. That is the story beind many of those forum posts about funny readings for a 10k thermistor in a 20k divider.

Why do they do this? They could just give us a bare input, and let us worry about driving the SAR.

What that large resistor does, is at least two things. For a packaged source device, and slow measurements, it might be good enough. It also makes it possible for a hobbyist, to be able to use the input in some instances, without thinking about it too much.

The problem with that approach, is that it also makes it impossible to use the ADC input a more correct way. And there is a limited set of circumstances where it works to give a realistic voltage.

So that is the story of analog inputs on MCU chips.
 
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