On Thu, 07 May 2015 11:45:01 -0500, you wrote: >The sensor is expecting a 5V signal on the trigger input and generates a >5V signal on echo. >You are feeding a 3.3V signal from the BBB and accepting a 5V signal >from the sensor. >Will the output of the BBB, 3.3V, be seen as a 5V input by the sensor?
The cmos threshold is 75% of VCC, so 25% of 5 volts is 1.25 volts, which gives a desired 1 threshold of 3.75 volts on the sensor. Not likely to see the signal as a 1. >Will the 5V signal from the sensor fry the gpio pin which is expecting a >max voltage of 3.3V? Yes. See the warnings in the manual. >This is just looking at the voltages and not considering currents, dig >out the spec sheets for the sensor to see what the voltage/currents are >that it is expecting. >The MOSFET level shifters will transform the 3.3V to 5V and vice versa. >Transistors/resistors will do the same operation. TI (and others) make unidirectional (can be switched for direction) level translators that protect both sides of the load and translate logic levels. The part number (typical) is something on the order of 74LVC8T245, IIRC. I'd recommend them highly. There are DIP packages more suitable for breadboards. Transistors can work, as can resistors, but the packaged device is a neater solution. Harvey >Chad > > >On 5/7/15 10:45 AM, claudiu [email protected] wrote: >> Well yes i do know that the BBB is a 3.3v with a 4-6 mA output. >> Therefore I have used the following configuration: >> |* TRIGGER P8_12 gpio1[12] GPIO44 out pulldown Mode: 7 >> * ECHO P8_11 gpio1[13] GPIO45 in pulldown Mode: 7 *** with >> R 1KOhm >> * GND P9_1 or P9_2 GND >> * VCC P9_5 or P9_6 VDD_5V(from BBB) >> | >> |but am I right ? | >> >> On 7 May 2015 at 16:23, doog <[email protected] >> <mailto:[email protected]>> wrote: >> >> >> On Thursday, May 7, 2015 at 1:44:57 AM UTC-7, claudiu <clip> wrote: >> >> For the sensor's VCC im using the VDD_5V from BBB. >> >> >> and you do know that the BBB is a 3.3v device so level shifting is >> probable? >> >> Doug >> -- >> 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/Cd9xj0AabcU/unsubscribe. >> To unsubscribe from this group and all its topics, send an email >> to [email protected] >> <mailto:[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. >> To unsubscribe from this group and stop receiving emails from it, send >> an email to [email protected] >> <mailto:[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. 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.
