Recent Posts

1

Test Equipment / Re: Choosing between entry-level 12-bit DSOs

« Last post by Fungus on Today at 12:19:53 pm »

There is no cheating. Just accept it.
It looks exactly the same if you single shot it.

What does single shot have to do with it?

You seem to be saying Rigol don't even know the basics of signal theory.

2

Projects, Designs, and Technical Stuff / Re: Homebrew Lock-In Amplifier

« Last post by RoGeorge on Today at 12:17:58 pm »

A LIA only works if you have a strong and clean reference signal, and in sync with the small and noisy signal to be measure, and only works at a constant frequency, or with very slow variations.  A LIA does not decode an unknown signal, it only averages the signal by a pattern given by the reference signal.

In regards to the max frequency, a classic LIA usually goes up to 100kHz or so, but they are very sensitive and very low noise in their analog input stage.  In contrast with that, the oscilloscope method is less sensitive, more noisy, but can work at frequencies as high as the oscilloscope can display, so virtually hundreds of MHz.  Which one to use depends of the measurement that needs to be done.

for basic experiments

For what kind of experiments do you need the LIA, what do you plan to measure with it?

3

Test Equipment / Re: Choosing between entry-level 12-bit DSOs

« Last post by Fungus on Today at 12:16:39 pm »

No, it does not have to be periodic. "Perfect reconstruction" only requires that the original signal sampled by the ADC sampled was bandwidth-limited.

Nope.

The signal in this image is bandwidth limited (5Hz signal, 11Hz sample rate) but sin(x)/x won't reconstruct it unless the filter is infinitely wide and the signal is periodic.

4

Projects, Designs, and Technical Stuff / Re: Homebrew Lock-In Amplifier

« Last post by Kleinstein on Today at 12:14:42 pm »

One can replace the AD630 with a CMOS swich (e.g. DG419) a few resistors and OP-amp.

For simple testing one should include some simple generator that also generate a quadrature signal. Many of the experents may wand a ref signal from a generator and it easier to start with 2 or 4 x the frequency and than make it an accurate 50:50 signal and get a quadrature signal than to generate this from a PLL. A simple µC to generatore the ref. signal and a source drive signal could be a good idea, as it allows to get at least some phase shift rather easy.

Parts of the design depend on how one looks at the output / result. E.g. when using an ADC there anyway, one would not really need the very long time constants at the output. The resolution at the output recording also determines how many gain steps and outout gain is useful. HIgh resolution there can substiture some gain steps.

5

Projects, Designs, and Technical Stuff / Re: Passing 2 wires into a hot water cylinder

« Last post by max_torque on Today at 12:11:13 pm »

When you measure the outlet (top) water temperature of a typical domestic hot water cylinder it's not a lot of use from a control perspective because it pretty much reads the same value until the tank is completely empty of hot water and then it suddenly reads close to the inlet water temperature!

This is because the water experiences a density change as its temperature changes, and the water at the top is always the hottest water, the incomming cold water simply sits below it.  Slowly over time, you find that top temp will fall as it looses heat to the colder water below it, but this isn't really enough to put in place much of a decent control system.

For example, my system pretty much sits at a top (outlet) water temp of between 55 and 50 degC, yet the 1/3rd point (1/3rd of the distance from the bottom) and the 2/3rds point experience much greater swings, and you can use them to estimate how much water is in the tank of any given temperature, ie the remaining capacity of the tank, and control heating as necessary.



The lower temperatures clearly show when hot water is drawn from the system, as the "slug" of cold water comes in, immediately drops the temp on the lower sensors, and then slowly warms up over the next few hours as the top temp drops very very slightly.  During heating, the lower temp jumps right up, by more than 20 degC, yet the top temp onyl changes a couple of degrees

6

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

« Last post by xvr on Today at 12:10:07 pm »

Ok, lets start from NDT3055L

Calculate for worst case 2 amp in parallel with steady on state. We have 12A load.
Rdson = 0.1OHm, so Voltage Drop on transistor is 12*0.1 = 1.2V, This is 6% of 20V, this is more than 5% of amplifier tolerance (as far as I remember) - transistor can't be used in this configuration

Let's try to calculate for 6A load.
Voltage drop is 6*0.1=0.6V. This is 3%, so your power supply should provide 20V +5%/-2% (quite tight but possible).
Power dissipation on transistor: P = I*V = 6*0.6 = 3.6W. This is quite a lot for smd chip without heatsink.
Temperature raise: P*Tja = 3.6*42 = 151C. Die temperature is 151 + 25 (ambient) = 176C. This is more than 150C maximum. So, transistor can't be used.

Now, let's try to evaluate for pulsed mode (2s cycle 50% duty cycle). By Figure 11 give coefficient 0.5 to Tj.
So, Tja will be 21, Die temperature is 3.6*21+25 = 100.6. In limits, but still too hot. Each 10 degrees of temperature raise reduce life time of transistor by 2 times.
And relaying for pulsed mode also dangerous - if some amplifier will be turned on for more than some time (10-100s approximately) transistor will be burned out.

Now check SiSS65DN.
Rdson = 4.6mOhm. Voltage drop (12A load) is 12*4.6e-3 = 55mV. Almost negligible from point of view of power supply for Amplifier.
P = 12*55e-3 = 0.66W. Max T raise 0.66*25 = 16.5C. Quite cold.

PS. 25 is worst case for Tja (from datasheet). But it specified for mounting on PCB with 1" copper area and for pulse less than 10s. DS do not contain information for steady state. But there is a large reserve in power and temperature, so steady state should not be a problem.

7

General Technical Chat / Re: Relay trigger when voltage above 13v

« Last post by NiHaoMike on Today at 12:03:30 pm »

Use a supply voltage monitoring chip, it will already have many features you want such as hysteresis and deglitching.

8

Embedded Computing / Re: WINCE question

« Last post by Bicurico on Today at 12:02:55 pm »

I don't see any issue. This is the embedded forum and we are talking about WinCE, which is for embedded devices.

The fact that the binaries run on a PC with Windows is within topic, I would say

9

EEVblog Specific / Re: EEVblog 1612 - Siglent SDS1000X HD 12 bit Oscilloscope Teardown

« Last post by 2N3055 on Today at 12:01:27 pm »

Hi Dave, my 1204X-HD has microphonic inputs.

Wow. Why the difference?

Perhaps they forgot to mount the capacitors in your unit.
Let them know and they'll happily ship you a couple that you can solder in place...

It is because Dave used 50Ω termination....

It is amazing how easier is to just speak smack instead of looking into facts...

10

Power/Renewable Energy/EV's / Re: DIY Battery Bank from Recycled 18650

« Last post by mtwieg on Today at 12:01:14 pm »

What are those things in a glass package? Fuses?

I assume they're fuses. I'd like to ask them why they're only used on specific cells...