I am newbie to electronics and just know a few basics. I want to switch on my DSL modem so it can start with my computer on. I think a transistor connected to USB +5V voltage would be simple and best. I will get base voltage from USB and collector voltage from modem DC adapter (about12 V and at 500mA). I am wondering which transistor is the best and how set base voltage. Thanks!
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\$\begingroup\$ I don't think a transistor is really the way you'd want to switch on an object like a preassembled modem... have you considered a relay of some sort that activates when your computer is turned on? \$\endgroup\$– justinrjyJul 19, 2015 at 14:45
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1\$\begingroup\$ I use a master-slave power strip for exactly this purpose. When I switch on my PC, the modem and some other peripherals follow automatically. Then again, I didn't enjoy the fun of making it myself. \$\endgroup\$– jippieJul 19, 2015 at 15:53
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\$\begingroup\$ Dear Justinrjy.yes and that will be set modem on. \$\endgroup\$– hamedonicJul 19, 2015 at 16:35
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\$\begingroup\$ Dear jippie .can you link me to that master-slave power strip? \$\endgroup\$– hamedonicJul 19, 2015 at 16:38
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2 Answers
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You (may) need a high-side switch to do this, which requires two transistors. Assuming the grounds are connected together (eg. a USB cable between the modem and the computer) you can use this circuit (left), or if the grounds are not connected, the right-hand circuit. :
simulate this circuit – Schematic created using CircuitLab
answered Jul 19, 2015 at 16:59
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\$\begingroup\$ Michael Karas .thanks and best wishes.I will try that \$\endgroup\$ Jul 19, 2015 at 18:20
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A relay as recommended in the comments would be a really good way to go for this if you want to build it yourself. It is a really simple solution and requires few components. It also provides isolation if that would be needed between the computer and the DSL modem.
Here is a picture of how to hook it up:
answered Jul 19, 2015 at 17:09
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\$\begingroup\$ Very impressive. The relay may be the best. I think this will not consume PC power. Yes? \$\endgroup\$ Jul 20, 2015 at 3:20
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\$\begingroup\$ As you can see in the diagram that the relay coil is connected directly across the USB 5V and GND. Power for the USB port comes from the PC so yes...some PC power is consumed. The G5V-1-DC5 relay that I showed in the diagram has a coil current rating of 30mA at 5V so that is 150mW that of power that will be drawn out of the PC. \$\endgroup\$ Jul 20, 2015 at 4:03
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\$\begingroup\$ Thanks Micheal. I think that 150mw consumed PC power is not so important. You rocks! \$\endgroup\$ Jul 20, 2015 at 12:29