3 replies to this topic

[boyse]

Hi all,

I've got the ADH8066 GSM module and the breakout board to go with it.

I'm trying to get it connected to my netduino so I can have a play - I'm new to electronics so any advice will be appreciated.

I'm powering the netduino using the USB, and I have 12v coming into the breadboard.

I'm using a LM350 voltage regulator circuit with R1 as 270ohms and R2 as 510ohms (as these are the closest resistors I have) to give an output of about 3.6v. This is used to power the ADH8066 module, which according to the datasheet needs between 3.4v and 4.5v.

Heres the bit I'm a bit stuck with - the datasheet says the recommended digital high voltage is between 2v and 3.14v, but further up in the extreme condition specification is says the max input/output voltage on any pin is 3.5v. I believe the netduino digital high voltage is 3.3v, so if I just connect the netduino digital out directly to the GSM module, will it harm it?
Should I use a resistor?
How do I calculate that resistor value as I don't think the datasheet gives enough information for that?
Could I build another voltage regulator circuit to output about 2.5v, and use a transistor connected to the digital out and the 2.5v rail to send the data? If so whats the best way to do this (which transistor?)?

Sorry for all the questions - I'm just trying to get as much info as I can so as not to blow up the GSM module or my netduino.

Thanks

Tom

[Mario Vernari]

Hello Tom.
The modem seems having a double voltage of operation, although only one must provided externally.
Your LM350 circuit is a good choice, since the best supply required by the modem should be 4V (strange value indeed).
BTW, the logic of the modem operates at different level: 3V (strange again).

In both the docs available in the Sparkfun site, there's a clear reference to +3V as the nominal high-level for the logic interface. Thus, yes...maybe the 3.3V given by the Netduino could be a little higher than the modem expect.

Well, *probably* you won't damage your modem nor the Netduino by connecting them directly. However, if you want to "sleep relaxed", you may provide a voltage divider as follows:

• from the Netduino out add a 10K resistor to the modem input;
• from the same modem input add a 100K resistor to the ground.

NOTE: that applies *only* form the Netduino output going toward the modem. For a modem output going toward a Netduino input, there's no problem connecting them directly.

Hope it helps.
Cheers

[boyse]

Thankyou! This helps a lot! Today I learnt about voltage dividers

[mwesigebrian]

Hello, 

I need help with a project that involves the use of a netduino 2, an SM5100B gsm/gprs module, a keypad and a solenoid valve that is normally closed. I am very new to this....the idea is for the netduino to be able to read a particular unique code phone number and amount of money sent via mobile money from the simcard on the gsm module and open the valve for a specified amount of time and then close....I am told i need to incorporate AT commands in the C# source code to get this working. I need help with the code