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| MadHacker | xobs: pcb rework? Had to change things much? | 07:41 |
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| xobs | MadHacker: reworking EVT1 boards to make them usable. It requires four bodges: two 0-ohm resistors to short, a spi flash chip to program and install (into a footprint that's slightly too small), and a crystal to install (into a footprint that's upside down) | 12:06 |
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| MadHacker | Ouch on the upside-down crystal. I've done that a few times. | 13:31 |
| MadHacker | If there's a smaller package available, it makes the wire routing for the bodge much easier. | 13:31 |
| xobs | Yeah. Turns out if you mount it on its side, you only need to run a power wire. | 13:31 |
| MadHacker | Using only 3 of the 4 pins? | 13:31 |
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| xobs | Yeah. The 4th pin is usually either "disable" and/or "NC", and can be left floating. | 13:32 |
| MadHacker | As you say. I've seen some peculiar variations, but the normal ones are fine left floating. | 13:33 |
| MadHacker | My Openbench logic sniffer has the clock crystal swapped out by one with reversed pinout, but I used a smaller package and just superglued it upside-down in the middle of the pads and tacked little bare wires (looks like bond wires, almost) from there to the board. | 13:34 |
| MadHacker | If you're gentle, you can probably roll over the SOIC pins for the flash into almost more like a J-leg pattern and have it fit the pad nicely. | 13:35 |
| MadHacker | https://www.golledge.com/products/gvxo-331l-3.3v-supply-voltage-controlled-oscillator/c-26/p-187 <-- the peculiar variations. VCXO in a normal crystal package, 4th pin offsets the frequency. | 13:45 |
| tpb | Title: GVXO-331L | 3.3V SM VCXO - Low Current Consumption| Golledge (at www.golledge.com) | 13:45 |
| xobs | Interesting. | 13:45 |
| xobs | The crystals I picked use the 4th pin as a "Standby" signal to stop the clock. | 13:45 |
| MadHacker | A lot of them just have it as a tristate output enable, rather than an actual standby. | 13:45 |
| MadHacker | The power consumption of those little 4-pin modules can be surprisingly high. | 13:46 |
| MadHacker | I used one on a board and found out the hard way (from the flat battery) that it drew about 15mA no matter what. | 13:46 |
| xobs | Ouch. That's almost more than all of Fomu. | 13:46 |
| xobs | Though the little linear regulators aren't the most efficient things. | 13:47 |
| MadHacker | The regs are really variable. I've had some that basically draw zero unless you load them, and some with 20-30mA drawn from the input no matter what. :/ | 13:47 |
| MadHacker | Unfortunately with almost identical part numbers. | 13:47 |
| MadHacker | One of those "read the damn datasheet, twice" lessons that was, again. Nearly buggered up a big event opening ceremony that way. | 13:48 |
| xobs | Hardware is hard that way. | 13:49 |
| tnt | xobs: which vreg do you use on fomu ? Some x2son ones or something smaller ? | 13:49 |
| xobs | tnt: Yeah, though I found two different vendors with footprint-compatible alternatives. | 13:50 |
| xobs | I don't remember if they ended up putting https://github.com/im-tomu/fomu-hardware/blob/pvt/reference/LDO-MIC550x-300mA-Single-Output-LDO-in-Small-Packages-DS20006006A.pdf or https://github.com/im-tomu/fomu-hardware/blob/pvt/reference/LDO-lp5907.pdf on | 13:51 |
| tpb | Title: fomu-hardware/LDO-MIC550x-300mA-Single-Output-LDO-in-Small-Packages-DS20006006A.pdf at pvt · im-tomu/fomu-hardware · GitHub (at github.com) | 13:51 |
| tnt | Ah yeah, that;s the footprint I was thinking of. I just used it on a PCB of mine and only realized how really small it was when came time to handsolder it :p | 13:54 |
| xobs | I used the SOT23 package for the EVT board to make it easier. | 13:55 |
| MadHacker | Quite a big difference on the current limit trip points on those; the TI one can trip at 250mA but the Microchip one won't trip until at least 400mA. Dropout's a lot higher on the microchip one too, at least under load. | 13:55 |
| tnt | ice40 consumes basically nothing in anycase. | 13:56 |
| MadHacker | tnt: The *core* consumes basically nothing. The I/O pins can eat plenty juice. | 13:56 |
| xobs | MadHacker: true, but the target current is about 20 mA. | 13:56 |
| tnt | sure, but the fomu has capacitive touch pads and that's it. | 13:56 |
| MadHacker | Surely 3x that from the LEDs? | 13:57 |
| xobs | The LEDs are current-limited to 4 mA each. | 13:57 |
| MadHacker | Fair enough. :) | 13:57 |
| tnt | Also, aren't the leds connected to vbus ? | 13:57 |
| MadHacker | tnt: You'd be over-voltage for the iCE40 I/O on the red if you did that, I think? | 13:57 |
| xobs | Technically you can pulse them at up to 24 mA each for 10% duty cycle. But I'm not doing that. | 13:58 |
| tnt | MadHacker: I was wondering that at first, but I've actually checked that the ice40 doesn't have the diodes to Vio rail on those 3 special pins. | 13:58 |
| xobs | The LEDs are connected to 3.3V. Which is over-voltage on the red, but since it's current-limited it should be fine. | 13:59 |
| tnt | xobs: that's the whole point of those IOs, they're current sinks, not normals IOs. | 13:59 |
| tnt | constant current sinks even. | 14:00 |
| MadHacker | There's still generally a limit on the input voltage though, so when they're in their off state, the input voltage can rise to the supply voltage. | 14:00 |
| MadHacker | So 3.3v is fine here, but 5v would be over the voltage limit on most iCE40 pins. Haven't checked the special rules for the LEDs. | 14:00 |
| xobs | tnt: right. I worried about that for a bit. But hooking up a scope and measuring it made me feel better. | 14:00 |
| tnt | xobs: :) | 14:00 |
| MadHacker | Checked, max is still 3.6 for those pins. So if you have a higher-voltage LED supply you might do bad things. | 14:04 |
| tnt | MadHacker: you still have the Vf of the led. The ice40 DS says that "Vdd - Vf < 3.6V" ... | 14:04 |
| MadHacker | Yep, although the Vf is the minimum leakage Vf, which is usually less than the "normal operating conditions" one. | 14:04 |
| MadHacker | (you can get a microamp through an LED at a lot less than the normal Vf; that won't blow things up but minus that protection diode you mentioned it'll cause electromigration and gate oxide stress and so on still) | 14:06 |
| MadHacker | Relatedly, some of the microchip PICs have internal shunt regulators, which let you run them off things like 48V DC supplies, just using a series resistor on the power input pin to bring the current into the shunt's control range. | 14:09 |
| MadHacker | Weird having a 5V *output* pin on a microcontroller, and doubly weird it being the same pin as the input pin. | 14:11 |
| tnt | The up5k eval board from lattice uses vdd=5v for the rgb led, but adds a shottky (Vf=0.3v @ 100mA so at low current, it would have virtually no drop either ...). | 14:11 |
| MadHacker | Interesting that they felt the shottky necessary. Wonder if the minimum Vf in the LED datasheet made them nervous. | 14:13 |
| MadHacker | Or if it's just reverse-polarity protection. | 14:13 |
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| tnt | I just measured the Vf of an "Off" led connected to the rgb pins of the ice40 and it was 1.4v drop, I guess just from leakage current. | 14:20 |
| tnt | (I guess technically my meter also added a tiny bit of current with 10M input impedance) | 14:20 |
| tnt | (That's also using the same led as the fomu) | 14:21 |
| MadHacker | Aye, so that's right at the absolute max spec on the part. | 14:26 |
| MadHacker | (if it were on 5v) | 14:26 |
| MadHacker | Actually a bit above; Vbus is allowed to be up to 5.25. | 14:26 |
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| xobs | By the way, I've added initial RGB Support to the experimental Fomu MicroPython port: https://github.com/xobs/micropython/tree/fomu/ports/fomu | 15:27 |
| tpb | Title: micropython/ports/fomu at fomu · xobs/micropython · GitHub (at github.com) | 15:27 |
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| futarisIRCcloud | xobs: Thanks. I'll try and a test it later today. | 23:06 |
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| xobs | futarisIRCcloud: I also got an updater written, discovered an issue with Foboot on certain devices, and added the ability to read the SPI ID. (These were all part of a yak shaving exercise.) | 23:59 |
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