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I use some level translators but it's not a solution (they take a lot of PCB and they are expensive ~2eu/4ch). I have the controller at 3,3v and SIM900 works at 2,8v. Another solution might be to use transistors instead of the level convertors.
do you want to use hardware already available or do you want to design a new one ? I'm asking because the hardware available from NI is quite expensive.
From SIM18 HD 1.02:
The slave has no way of forcing data to the master to indicate it is ready for transmission; the master must poll the client periodically. Since the specified idle byte pattern for both receive and transmit is A7 B4, the master can transmit this idle pattern to the slave...
use CD4066 or some other equivalent, it works great and it's cheap. you can also use a MCP6S28 if you want to have something with SPI and gain selection (see documentation).
No, I didn't, I will use a SIM908-C for the final project and I abandoned researching this problem. Interesting fact: It stays OFF after I apply the voltage and I can power it ON only by touching a metal thing on the PWR pin... If I try to power it ON or OFF in the normal way (as in...
I tried that in the first place and wasn't working, that's why i started investigating and tries all the stuff that I tried. With the transistor is not working either.
When I said that the pin goes low I meant with the pin left floating without any transistor connected (I powered it OFF with the power off command because by pulling the pin low wouldn't work). If it has a pull up resistor wouldn't still be at high level regardless of the state of the modem's...
Hello,
I'm designing a board for some GPRS communication. The module works fine so far but if I want to turn it OFF it wont stay OFF and after 10 sec it powers ON by itself. Also I cannot power it OFF from the power key pin, the only way is to send the AT+CPOWD=1 command. After this command it...
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