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Test Equipment / Re: Vevor SDS1104 for first oscilloscope?
« Last post by tautech on Today at 06:39:37 am »well, if you need 4CH: go for the Siglent SDS1104 -- best bang for the buckWas.
Now SDS804X HD is.
Recent Posts
Now SDS804X HD is.
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General Technical Chat / Re: Do you think an LED is a resistor?
« Last post by magic on Today at 06:36:31 am »From: A.C. Fischer-Cripps, in Newnes Interfacing Companion, 2002
3.3.7 Log amplifier
A non-linear resistor is connected into the feedback circuit. In practice, this can be a diode, but a transistor connected as a diode is used since the forward biased transfer function is more accurately exponential. The exponential nature of the forward biased diode leads to a logarithmic decrease in gain of the circuit as the input signal is increased.
Nonsense.
This circuit has almost linear decrease in gain as the input signal increases. Consider for example R1 = 1kΩ:
Vin = 1V, I = 1mA, Vout = -600mV, gain = -0.6
Vin = 2V, I = 2mA, Vout = -618mV, gain = -0.31
Vin = 5V, I = 5mA, Vout = -642mV, gain = -0.13
Vin = 10V, I = 10mA, Vout = -660mV, gain = -0.066
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Test Equipment / Re: DMM Input Capacitance
« Last post by ebastler on Today at 06:35:12 am »I have a convenient outlet on my bench, so I used a hex key inserted as my ground reference.
I kind of like the idea of having an outlet right in the benchtop for testing. (My main power strip is below the benchtop, hence a bit inconvenient to reach when I want to plug/unplug a DUT often.) In practice, how often do you drop clipped wire ends and stuff into the mains and USB outlets?
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Test Equipment / Re: Siglent SDS3000X HD and upgraded SDS1000X HD
« Last post by H.O on Today at 06:30:36 am »Mine too, a few weeks back.
Still, 500MHz probes delivered with a 100MHz scope - can't complain.
Still, 500MHz probes delivered with a 100MHz scope - can't complain.
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General Technical Chat / Re: Do you think an LED is a resistor?
« Last post by ebastler on Today at 06:24:19 am »Sheesh... how long do you guys plan to continue this?
"Resistor", without any qualifier, is used in practice to designate a component which exhibits ohmic resistance. Strictly speaking, one should use the term "ohmic resistor" for that type of component, and reserve the unqualified "resistor" as the generic term for ohmic and non-linear resistors. But in practice, nobody does that.
We also use special terms for non-linear resistors with specific properties -- diode, varistor, NTC, PTC etc. -- and don't refer to them as "resistors". Otherwise, confusion would ensue since "resistor" is so commonly used to refer specifically to ohmic resistors.
So Sredni is right, in a fundamentalist, "how many angels on a pinhead?" kind of way -- which seems to give him great satisfaction. But in practical terms, everybody else is right.
"Resistor", without any qualifier, is used in practice to designate a component which exhibits ohmic resistance. Strictly speaking, one should use the term "ohmic resistor" for that type of component, and reserve the unqualified "resistor" as the generic term for ohmic and non-linear resistors. But in practice, nobody does that.
We also use special terms for non-linear resistors with specific properties -- diode, varistor, NTC, PTC etc. -- and don't refer to them as "resistors". Otherwise, confusion would ensue since "resistor" is so commonly used to refer specifically to ohmic resistors.
So Sredni is right, in a fundamentalist, "how many angels on a pinhead?" kind of way -- which seems to give him great satisfaction. But in practical terms, everybody else is right.
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Test Equipment / Re: My poor mans SMU - The Agilent 66311B
« Last post by vaualbus on Today at 06:15:27 am »Nope any of the 663xx series is gpib only unfortunately. You have rs232 in the 663x series.
As said this is another reason why to hack the fw to support serial also on this series.
As said this is another reason why to hack the fw to support serial also on this series.
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Beginners / Re: audio amp study
« Last post by dietert1 on Today at 06:13:42 am »The difficulty to adjust bias probably indicates oscillation. The schematics presented above are missing a local buffer cap for the supply. When using test leads for the supply, this missing cap can already cause instability and oscillation.
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Projects, Designs, and Technical Stuff / Re: Short (1ms) high current (~200A) current pulses - relay rating?
« Last post by Berni on Today at 06:04:53 am »Update: Change of plan!
Going to use a crowbar relay that is not is series with the output, but in parallel with it. So when the Estop is hit (or power is removed from the device), not only will i de-power the switch mode convertor that generates the 250Vdc, i'll drop a crowbar across the output capacitor to ensure it is discharged and cannot be charged. As the device will be connected to DUTs that run at up to 33vdc, i'll probably use some big 40V TVs diodes and a low value power resistor to quickly drop the output voltage below 50Vdc (as required by the Low Voltage directive)
This means my output path from the pulse caps is now just across the output control switch which is a semi-conductor switch
That is indeed a better solution.
Tho the thing to watch out for is closing that relay while the capacitors are still very full. Be it because a wire going to your DUT fell off, or the DUT failed open quickly. Closing a relay directly across the charged capacitors has a very high chance of welding relay contacts with the huge initial pulse current. The relays are most vulnerable to being damaged during switching (due to switch bounce), once it is fully closed, it can handle very large peak currents.
Perhaps it is adequate for your solution to have the relay connect a low value resistor across the capacitors. Then pick a value that will discharge the capacitor with a few 10s of Amps just below what a regular small relay might survive without welding, yet have the resistor be low enough in value that the charging circuit is not powerful enough to charge up the capacitor to any meaningful voltage with the resistor applied.
Nice thing is also that if the relay welds, it fails stuck into the safe state
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Other Equipment & Products / Re: Dymo 550 Thermal Printer DRM Hacking
« Last post by oztek on Today at 05:55:14 am »Hi Everyone,
We have a Dymo 550 Turbo we purchased as a replacement to a dead older Dymo.
It's used as a workshop label printer, as we have a large supply of generic 30252 address labels with removable adhesive, the dymo equivalent are permanent adhesive.
Initially we kept using our labels by ripping off the RFID sticker from a genuine roll until the count ran out.
I've tried very hard to get this bluepill solution to work and I'm not having any luck. I wondered if I had perhaps bought a counterfeit bluepill board so I bought some more from one of the amazon links posted on this forum to try again.
As we are only going to be using 1 label type, the RFID board is not attached.
I've used an ST-LINK V2 to flash on the pre-compiled freedmo-default-sku-30252.bin.
The process appeared to work successfully, I saw the memory contents change to match the file, and I've tested reconnecting and reading it to confirm it updated.
RFID board is removed from the printer and the bluepill plugged in it's place - printer is detected in windows, but when trying to print we still get an unknown label detected error.
Can anyone please help, or spot something I've done wrong?
Thanks
We have a Dymo 550 Turbo we purchased as a replacement to a dead older Dymo.
It's used as a workshop label printer, as we have a large supply of generic 30252 address labels with removable adhesive, the dymo equivalent are permanent adhesive.
Initially we kept using our labels by ripping off the RFID sticker from a genuine roll until the count ran out.
I've tried very hard to get this bluepill solution to work and I'm not having any luck. I wondered if I had perhaps bought a counterfeit bluepill board so I bought some more from one of the amazon links posted on this forum to try again.
As we are only going to be using 1 label type, the RFID board is not attached.
I've used an ST-LINK V2 to flash on the pre-compiled freedmo-default-sku-30252.bin.
The process appeared to work successfully, I saw the memory contents change to match the file, and I've tested reconnecting and reading it to confirm it updated.
RFID board is removed from the printer and the bluepill plugged in it's place - printer is detected in windows, but when trying to print we still get an unknown label detected error.
Can anyone please help, or spot something I've done wrong?
Thanks
10
Test Equipment / Re: Vevor SDS1104 for first oscilloscope?
« Last post by andrewtaylor on Today at 05:44:42 am »well, if you need 4CH: go for the Siglent SDS1104 -- best bang for the buck 