| Electronics > Beginners |
| Transistor selection confusion |
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| Zero999:
--- Quote from: phaseform on May 23, 2018, 09:06:13 am ---so yes, I am using a BC546, BC639 is one I had already and decided it was not ideal, so I got some BC546 parts.. D0 is giving 0.3 V low, and at least 1.5 V high (up to 2.7 V no load), D0 varies with sensor current, and isn't really a digital signal in my config at least. I played around with the adjustment pot and that's the best I could get, don't fully understand how the tuning worked. I went and got one of these arduino compatible relay boards because I wanted the SSR switching to be discrete (on/off), it draws 150mV through the sense pin over a 10 Ohm resistor = 15mA (wired as: 5v - resistor - relay board sense pin). So next is to figure BC546 (derp) resistor values to trigger this relay board for >= 1.5 V D0 output... it will have to wait for now. So much for a simple project... as with every case. --- End quote --- Something is wrong with the current sensor board or power supply. The digital output should be more than 2.7V, unloaded and it should be independent of the potentiometer setting. Have you checked the sensor board is actually getting 5V? Are you sure you're not measuring the analogue output? The circuit I posted previously will work fine at lower input voltages. It will probably still work with 3k3 to 4k7 and an input voltage of 2.7V, since the Hfe of the transistor will be well in excess of 10. If the SSR still doesn't activate with it, then reduce R1 to 2k2 or 1k8. |
| phaseform:
I think the sensor board is causing all the issues here... If I run the digital sensor output to the input of the arduino relay board, I get the relay switching on/off at what i guess is line frequency. Even if I only put 2.6v DC into the relay (5v through a resistor), it will trigger, with a dimly lit indicator LED, that same voltage from the sensor output will cause the relay to switch on/off like crazy. I tried some random electrolytic caps to smooth this to no avail - haven't tried finding a correct filter cap as a potential solution.. re the sensor board: Around the middle of the adjustment pot, I get: no current: 5.2v light off high current: 2.9v light on other setting: no current: 0.3v light on high current: 2.7v light dim those values are around the middle of the trimpot, and have the greatest change in voltage. The analog output was just noisy to my DMM |
| Doctorandus_P:
You're going to a shop to buy a single transistor? Sounds weird, unless it's some special transistor. I can highly recommend a "transistor assortment kit" from Ali / Ebay / China / Whatever. 300 or 600 transistors ifn different sizes and polarities. Always fun to experiment with, and no harm done if you let some of the magic smoke out. Your first job would be to get the datasheets of the transistors involved. Then make some comparisons, and select a nice kit on the bases of the selction in the kit. There are quite some differences between those kits. |
| phaseform:
nice, I'm just going pragmatic :-// rather than get too far into dealing with whatever this sensor is handing out, without buying a scope |
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