This DAC has a flexable input voltage option. So if I'm inputing a 3.3V voltage to it, by controlling via I2C, I can get a 0~3.3V linear voltage output. That 5V power source is just for powering the relay and the BBB & touch screen. So I don't think I'm driving a 5V circuit with BBB. On the other hand, I think the BBB can also output 5V, so I can as well give the DAC a 5V directly from BBB, right?
2015-10-28 23:30 GMT-04:00 Bill Pretty <[email protected]>: > After just a quick look at the circuit, I suspect that the BBB is trying > to source/sink too much current? > > > > Also, the BBB has 3.3V logic and you are driving 5V logic. I would suggest > that you use an opto-isolator > > for both isolation and logic level conversion. > > > > Bill > > *From:* [email protected] [mailto:[email protected]] > *On Behalf Of *Yongfan Men > *Sent:* Wednesday, October 28, 2015 10:58 PM > *To:* BeagleBoard > *Subject:* [beagleboard] Re: My circuit that burnt my BBB needs modify: I > wonder if the ground is necessary > > > > Forgot to attach the illustration figure. > > On Wednesday, October 28, 2015 at 10:41:36 PM UTC-4, Yongfan Men wrote: > > > I burnt my BBB, which let me very sad. I ordered a new one online because > it's an urgent project, but until I have fully figured out what happened > with my circuit, I dare not connect the BBB to it again. > > > > This circuit, as shown in the attached image, worked all well during the > last whole week. I turned it off this Monday, and turned it on this > morning, and Bang! The BBB's burnt. It won't boot up. When I plug the 5V > power cable or mini USB cable to it, only the PWR LED will light up a > little bit, and it never boots up again. I didn't believe it's my circuit's > fault, so I plugged my backup BBB on, and again, it's killed. I burned $100 > in 10 minutes. > > > > I'm attaching the circuit design here because I need to know if this > design is really problematic. Let me explain a little bit: I'm trying to > control an I/P converter (SMC ITV0011), which is driven by a 0-5V voltage > signal and powered by 12V dc. *The problem is It only has three wires, > and the ground wire is shared.* That's why I think I have to connect all > of the ground wires together. > > > > I'm using a DAC chip (MCP4725) to generate a proper voltage control signal > to the I/P converter. This DAC chip is communicated by I2C, and powered > directly by the onboard 3.3V from the BBB. I have carefully checked with > multimeter that with digital command through I2C, the voltage could be > linearly generated, which is very cool. > > > > I'm using a GPIO to control a relay (powered by 5V) to control the on/off > of the I/P converter, which means only when I want the I/P converter to be > turned on, I will send the GPIO to 1. Otherwise, when GPIO is 0, the I/P > converter would not be powered, which is a way of enlarging the lifetime of > the $200 I/P converter. > > > > That's the whole idea. And I also used a Qt GUI to control the output of > both the I2C and GPIO. Last week, I enjoyed a lot using the stylus to drag > the slidebar on the touch screen to adjust the pressure output by the I/P > Converter. I just don't understand why it suddenly became so dangerous. > > > > But last week I did noticed one strange phenomenon. When the relay was not > working, there is a strange minus 17 volt on the relay output port. This is > probably 12V + 5V, But I don't understand neither why this is a sum nor why > it is negative, and since everything works, I didn't pay attention. > > > > Today, after I burned the two BBB, I measured the voltage of the relay > output port when it's off again. The voltage is 1.7V (5V-3.3V?). So strange! > > > > From my newbie understanding, any output signal should has two wires, one > signal wire, and one ground wire. Because you need a closed circuit to > transfer electrons. That's how coaxial cable works for oscilloscope, and > function generator, and multimeter, and so forth. Therefore I'm connecting > the GND from BBB to DAC, and the GND from DAC to I/P converter; also the > GND from 12V dc power source to the I/P converter. *This equals that the > Ground from the 12V dc power source is directly connected to the BBB*. > But theoretically, I don't see any problems, since it's just ground! > > > > In the image, I think once I remove the red wire, the BBB will be isolated > from the whole 5V and 12V dc circuits. But I don't know if this is the > right solution, and also if the voltage output from the DAC will be > transfered to the I/P converter. If any of you could explain a little bit > about this issue, I would appreciate a lot. > > > > Also, If I want to add some more protection to the BBB (on both I2C and > GPIO), what should I do? Thanks! > > -- > For more options, visit http://beagleboard.org/discuss > --- > You received this message because you are subscribed to the Google Groups > "BeagleBoard" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > For more options, visit https://groups.google.com/d/optout. > > -- > For more options, visit http://beagleboard.org/discuss > --- > You received this message because you are subscribed to a topic in the > Google Groups "BeagleBoard" group. > To unsubscribe from this topic, visit > https://groups.google.com/d/topic/beagleboard/wx6zQr_SaFE/unsubscribe. > To unsubscribe from this group and all its topics, send an email to > [email protected]. > For more options, visit https://groups.google.com/d/optout. > -- For more options, visit http://beagleboard.org/discuss --- You received this message because you are subscribed to the Google Groups "BeagleBoard" group. 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