Recent Posts

1

Beginners / Re: Comparator problem

« Last post by xvr on Today at 11:54:19 am »

> What if the input pulse amplitude is expected to span from 0 to 5V? What would be the strategy for the bias in this case?

Set small bias (about the same 0.5V) and add protection schottky diode from comparator input to ground (anode to ground, cathode to input)

2

Beginners / Re: buying a oscilloscoop

« Last post by Wallace Gasiewicz on Today at 11:54:17 am »

Before you buy scope probes make sure that the probes  capacitance matches your scopes input. I did not see the values of the 2 KV probes capacitance in the link.

3

Projects, Designs, and Technical Stuff / Re: Looking for a sensor to detect burning "smell" of coal and wood

« Last post by RoGeorge on Today at 11:52:55 am »

There was an article on Hackaday, about a commercial device that was monitoring air quality + radiation levels, and if allowed, the software was also uploading the data in a global network of air and radiation monitoring.
https://hackaday.com/2015/12/07/globally-distributed-sensor-net-monitors-air-quality-and-radiation/

The author (Radu Motisan https://hackaday.io/radhoo) turned that into a business later, and the device evolved with time, maybe now they detect air smells, too.  This one is from 2017:  https://hackaday.io/project/8334-city-air-quality

4

Beginners / Re: Switching a 3KW (240V) immersion heater: Solid state or mechanical relays?

« Last post by Gyro on Today at 11:50:39 am »

A followup question about this, the usual-suspect electrical suppliers, meaning ones who provide the necessary SDOC, can only provide the 2xNO with a minimum order quantity of five while they have 1xNO, 1xNC in stock in single-unit quantities.  If I source it myself from Farnell or whatever it won't come with an SDOC.  Given that I'm only switching a pure resistive load that heats water rather than, say, turning limb-removing power machinery off, so even if contact welding occurs it's no big deal, is it worth going to the 2xNO supplied-by-user to switch active+neutral or is it good enough to use the 1xNO with SDOC to switch active only?

Also, am I overthinking this? :-).

A double pole wall mounted mechanical isolator switch/ cable outlet is required for immersion heaters (well it is in the UK anyway), that should already be in place. A single pole relay / contactor should be sufficient for this 'auxiliary' function. I believe the internal thermostat inside the immersion heater only uses a single pole contact.

5

Projects, Designs, and Technical Stuff / Re: role of optocoupler for biasing drain of amplifiers

« Last post by john23 on Today at 11:50:31 am »

Hello ,according to the datasheet (photo shown in the link)I have to put 20V on the drain(which is the source of the NDT3055L mosfet) of the TGA2590 power amplifier that means i need to put
20V on the source of the mosfet.
You said that its a floating voltage without reference ,how do i make sure i have 20V on the source of the mosfet (drain of TGA2590) as shown in the diagram below.
Thanks.

https://www.qorvo.com/products/p/TGA2590-CP

https://ibb.co/SfNRtJy
https://ibb.co/xgF5VL0

6

Beginners / Re: Comparator problem

« Last post by elki on Today at 11:50:22 am »

What if the input pulse amplitude is expected to span from 0 to 5V? What would be the strategy for the bias in this case?

>  where does this 0.5V come from

It's your input pulse amplitude (from OP)

7

Beginners / Re: Comparator problem

« Last post by shapirus on Today at 11:49:45 am »

Bias should be at least 0.5V (or more). Now your input pulse generates negative voltage on comparator pin.

And then the 0.1V threshold voltage will always stay below the voltage on the non-inverting input.
later edit: maybe it'll actually be all right. Needs simulation, I'm failing to put it together in my head at the moment :)

One way to avoid applying too low a negative voltage to the non-inverting input pin is to connect a Schottky diode from ground to the non-inverting input.

At this point it becomes cumbersome enough so that the solution suggested earlier to use a resistor divider to bring the input signal level in the suitable range (around 2.5 V) starts to look more attractive. Of course, the threshold voltage source will then have to be adjusted accordingly.

8

3D printing / Re: could anyone please print me a microscope Head adaptor ring

« Last post by davebb on Today at 11:48:20 am »

Hi mendip_discovery
i have not had any contact from you lately, is every thing ok
i hope all is ok,
Thanks Dave 2E0DMB

9

Beginners / Re: Comparator problem

« Last post by xvr on Today at 11:47:26 am »

>  where does this 0.5V come from

It's your input pulse amplitude (from OP)

10

Beginners / Re: Any help? Raspberry Pi prod counter w/ reflective sensors - output concerns

« Last post by BeBuLamar on Today at 11:46:04 am »

And I under the impression that you have all the PLC parts needed. You have Sick and Banner sensors. You have Allen Bradley power supply. So I guess you have an Allen Bradley PLC laying around some where.