Going backwards, can't even get a basic blinky working now

[Ioannis]

I guess you have biased the MCLR pin, right?

Ioannis

[aerostar]

Why don't you get rid of the crystal and use the pic internal oscillator ? That should stop your hand capacitance causing problems on the crystal circuit.

[tumbleweed]

Regarding the overshoot issue, if your PICkit 4 is serial number BUR20xxxxxxx or later (-R2) then it has a mod in it to reduce the overshoot so it's not as much of a problem. Before that, they used to recommend using a 470R in series with the PK4 MCLR connection to the target.

From ETN37:

Some PIC16/18 devices have options to use high voltage on VPP or NMCLR to program the device. On some
devices, the VPP/NMCLR pin has special ESD protection. Overshoot on the pin can result in a reset condition or
current consumption outside of the specification. To avoid this situation, the data sheets for these devices
recommend the use of an RCR network with a pull-up, a power up charge capacitor and a series resistor
configuration into VPP. A series resistor of 470 ohms is used to dampen any overshoot and to limit current into
VPP/NMCLR

[Demon]

Regarding the overshoot issue, if your PICkit 4 is serial number BUR20xxxxxxx or later (-R2) then it has a mod in it to reduce the overshoot so it's not as much of a problem. Before that, they used to recommend using a 470R in series with the PK4 MCLR connection to the target.

From ETN37:

BUR223673449


Do you mean -R like a command line? Taken from the IPECMD docs:

R<on><off>

Safe/Restricted mode (Applicable only for MPLAB PM3)

Default = None

I'm running the PK4 from MCS+5.

Robert

[tumbleweed]

BUR223673449

Then it has the mod to address the ETN37 overshoot issue.

Do you mean -R like a command line?

No, I meant the PK4 assy number... usually on the label right above "BURxxx". On one of mine it's "10-10094-R2"

There's probably no real reason to put a zener on VDD. The overshoot was only on the VPP/MCLR high-voltage generator.

[Demon]

Then it has the mod to address the ETN37 overshoot issue.

No, I meant the PK4 assy number... usually on the label right above "BURxxx". On one of mine it's "10-10094-R2". ...

Mine is up to -R6.

... There's probably no real reason to put a zener on VDD. The overshoot was only on the VPP/MCLR high-voltage generator.

I wasn't really thinking of protecting VDD from the PK4. This was more to protect the circuit from being driven by who-knows-what wall-adapter by a user.

Robert

[Demon]

Talk about varying absolute maximum specs from one PIC to another:

16F877
Voltage on VDD with respect to VSS.................+7.5V
Voltage on MCLR with respect to VSS...............+14V

Was plan A, but I'm forgetting about the 16F877; keeping it for disposable pet projects now. I've wasted enough days trying to figure what I'm doing wrong.

18F4550
Voltage on VDD with respect to VSS.................+7.5V
Voltage on MCLR with respect to VSS...............+13.25V

Gotta be prepared to use this series, in case I ever get the C++ USB code figured out.

18F26K22
Voltage on VDD with respect to VSS.................+6.5V
Voltage on MCLR with respect to VSS...............+11V

This is my plan B unless there's something even sweeter out there, has 2 USART circuits. I could use one to talk to the PC via USB, and the other to talk with other PICs. Starting to test these as soon as my ZIFs come in. I'm making my own soldered test boards; not trusting the Lab-X1 with its funky blinking for no apparent reason.


I wish I knew absolute specs varied this much before; I never paid much attention to that. I've already put in a few order to DigiKey, Newark and Mouser for all sorts of odds and ends;including some Zeners.

Robert

"I'm killing the planet single-handedly with shipping."

[Demon]

I guess you have biased the MCLR pin, right?

Ioannis

I don't know the term "bias" in relation to the MCLR pin; but if you mean put a zener upside down so it breaks down over a given voltage, then yes, I'm biasing the pin.

Scroll down here to the paragraph called Zener Transient Suppression.

https://www.electronics-tutorials.ws...ppression.html

I'm going to go one step further with zener diodes. I'm gonna add a 1N5243BTR on MCLR to break down at 13 volts, and a ‎1N5232BTR on VDD to break down at 5.6 volts (specs say 5.5V is "max" - but I figure they're leaving a small margin for safety).

Unless someone has a good reason why I shouldn't...?

Why don't you get rid of the crystal and use the pic internal oscillator ? That should stop your hand capacitance causing problems on the crystal circuit.

I'm not seeing an internal oscillator on the 16F877: LP, XT, HS and RC. If you mean RC, it uses a capacitor as well. Won't that cause the same issues? They also mention other issues, like accuracy/tolerance of the resistor and capacitor, as well as temperature.

This will ultimately run a USB or USART connection as fast as I can.


I've tested the new breadboard using two gold pins from a header as probes (those pins are thick, clean and square) and I'm still getting a lot of "looshish" spots in some areas. The much thinner pins on capacitors, oscillators and some resistors must definitely be messing up my circuit.


Also, I think I have some capacitor/interference issue with my Lab X1 as well (probably not even related with my breadboard issues, just bad timing). Waving my hand over the X1 should not affect operations. It's possible it now has a defect; I bought it when they came out.


I'm looking at using fiberglass breadboards and soldering my components. I've been thinking of making my own Arduino-ish circuits for testing for a very long time. This might be the time to give that a try.


Side note: the tips on my Aoyue 738 soldering station are garbage. Bought some new ones on Amazon and they just don't last. One comment on the listing was "I've had packs of gum that lasted longer"; he wasn't exaggerating.

I bought new soldering paste since mine was 20 years old and had spent winter in unheated garage. I've just received today one of those brass brush balls to clean the tip; hoping that works better than that water sponge (never liked that).

Robert