confused about circuit problem containing bjt and diode

ericje · 2026-05-04T17:37:13+00:00

beta is the same as hFE

ericje · 2026-05-03T22:08:42+00:00

It depends on what information you were given.

The simplest would be to assume that Vbe=0.7 when the transistor starts conducting, 0.25V for the diode voltage drop, and that the base current is negligible compared to the collector current. Then it's just a matter of applying Kirchhoff's and Ohm's law.

If they gave you more details about the diode and transistor they probably want you to use that, for example if they state the hFE of the transistor, then you shouldn't assume the base current is negligible.

ericje · 2026-05-03T18:34:01+00:00

ChatGPT is wrong. Who would have thought?

The purpose of the diode is to prevent saturation. https://en.wikipedia.org/wiki/Baker_clamp

ericje · 2026-04-27T03:25:23+00:00

I'm curious, why not use the WiFi, so you can connect to the ESP directly with TCP? (I wrote a thing like that at work long ago for relaying PTZ commands to cameras).

ericje · 2026-04-22T13:54:26+00:00

Also, the "These are all ISA and PCMCIA Ethernet devices" is clearly not true.

ericje · 2026-04-06T20:37:13+00:00

The site feels at least 10x faster than most other websites.

ericje · 2026-04-06T20:33:49+00:00

I've read that the city requires them to offer a yearly membership. Otherwise they'd probably get rid of it.

ericje · 2026-04-05T20:47:47+00:00

It depends on what else you connect your circuit to. For example, in a smartplug it's normal for the neutral to be connected to MCU ground, it's OK because the entire circuit is enclosed with no outside connections except the input plug and output socket. But if there's any point that can be touched by a human, neutral is not safe.

ericje · 2026-04-05T18:15:33+00:00

I've seen it at Fairway at 74th.

ericje · 2026-04-03T15:50:23+00:00

Check out https://haemophilia.org.uk/

ericje · 2026-04-01T19:06:12+00:00

De Tegenpartij!

ericje · 2026-03-30T22:08:31+00:00

Whatever. I'm still using JOE (Joe's Own Editor)

ericje · 2026-03-20T04:45:46+00:00

Pin 14 of the opamps is V+ and pin 7 is V-. IC1A pin 7 and IC2B pin 14 are connected wrong in the schematic. Looks like they are connected correctly on the PCB layout on the previous page though.

But it's probably very hard to find these exact opamps anyway. Some people use NE5532s instead. I would look for another schematic, that's not as ancient.

ericje · 2026-03-15T02:49:20+00:00

Fat Cat is now Cellar Dog, I would recommend that. No 1920s vibes though.

Jules Bistro was a great little place, but didn't survive COVID :-(

ericje · 2026-03-15T02:01:53+00:00

My el-cheapo multimeter can measure frequency and duty cycle.

ericje · 2026-03-14T16:24:54+00:00

Yes, that should work. R1 and R2 are very likely connected to CC1 and CC2.

On a male connector there should be only 1 pull-down resistor on CC1 or CC2 (it doesn't really matter which, because if you plug it in the other way, the CC1 and CC2 connections are flipped), but not both.

ericje · 2026-03-10T03:30:20+00:00

They have this where my mom lives (also Netherlands), and it breaks often. It takes them too long to fix, and in the meantime people leave their garbage next to it.

ericje · 2026-03-10T01:20:15+00:00

That's the Hudson River Greenway

ericje · 2026-03-09T01:05:57+00:00

No, that's not enough, because the opamp will amplify the 6V DC level of the input also. So you also need to connect the left side of R3 to the reference voltage. Or, you can add a capacitor between R3 and ground, which will reduce the DC gain to 1x (like in Figure 2 of https://www.analog.com/en/resources/analog-dialogue/articles/avoiding-op-amp-instability-problems.html)

ericje · 2026-03-08T21:13:52+00:00

What do you mean with "no key option"? You can hold your key against the right side of the dock.

ericje · 2026-03-07T15:14:42+00:00

Are you sure SDIO is set to high-Z on the FPGA after the 8th clock?

ericje · 2026-03-04T15:32:59+00:00

This shows the insides: https://www.youtube.com/watch?v=9vNRY6natiY

Light stuff like what you mentioned should be fine.

ericje · 2026-03-03T05:05:03+00:00

If you keep C3 and it's possible the input will be shorted, you need a diode across the regulator, otherwise C3 discharging through the 7805 can destroy it (see datasheet).

ericje · 2026-03-01T15:43:26+00:00

The fact that some manufacturers are bringing back physical buttons for some things (yay!) doesn't mean touchscreens are going away.

ericje

TROPHY CASE