#45-1~3, H2: 4G (LTE) Modem

Function: 4G (LTE) modem

Form factor: H2

Category: Input/output module

Special needs: [SER]

Power requirements: 5V/500mA average, peak current consumption reaches 2A

Temperature range: –40°C to +85°C

Mates with: ---

See also:#46, #47

Details

This Tibbit comes in the H2 hybrid form factor and is based on the SIM7500 LTE CAT-1 family of modems manufactured by SIMCom. It features an SMA connector on the front for use with an external antenna, which is not included with the Tibbit but is required for it to operate.

The modem has standard TX, RX, RTS, and CTS signals, as well as several additional control lines.

Control Lines

This Tibbit has four control lines:

• –SDWN (shutdown): When LOW, turns off the Tibbit's power regulators. When the line is switched to HIGH, the power regulators are enabled, but the modem remains off.
• PWRKEY (power key): A LOW-to-HIGH transition on this line toggles the power on and off; it turns the modem on if it was off or off if it was on. Toggling the module on requires keeping a HIGH state of signal (after a transition from LOW) for about 500ms (see Fig. 1). Turning the module off requires keeping a HIGH state for about 2.5 seconds (see Fig. 2).

• STATUS: This line is LOW when the modem is off and HIGH when it is on. This line can be used to check the current power state of the modem. It takes at least 22 seconds for the STATUS line to reach HIGH after the modem is powered on, after which the module can begin operating. There are two methods of determining whether the modem is on or off: by sending an AT command and checking for a response or querying the STATUS line's state. Note that the line's state is undetermined when the modem is shut down (i.e., the –SDWN line is LOW).
• RESET: Bringing this line HIGH for about one second resets the modem. There is no need to reset the modem after turning on its power.

Before establishing a connection, the modem should be initialized. First, pull the –SDWN line HIGH to enable the power regulators. Next, toggle the PWRKEY line HIGH for about 500ms to turn on the modem. After the STATUS line goes HIGH, the modem is ready to communicate using AT commands via a standard UART interface with RTS/CTS flow control. At this point, you can decide whether to allow the system to establish a PPP connection automatically or to remain in AT command mode (see the Library section below).

SIM Card Slot

The card holder of Tibbit #45 accepts a 4G LTE micro-SIM card and features a “close-and-slide” locking mechanism. The card holder is located on the bottom of the Tibbit, meaning that insertion or removal of the SIM card requires opening the Tibbo Project Box enclosure and removing the Tibbit from the Tibbo Project PCB (TPP). We chose this relatively inaccessible location for the SIM card to reduce the chances of theft — accessing the card holder requires quite a bit of time and work, making it impossible to remove the card surreptitiously.

LEDs

There is one red and one green LED. The red LED is connected to the TX line, while the green LED is linked to the RX line. The remaining lines are not equipped with LEDs due to the internal board’s space constraints.

Power Considerations

At full LTE bandwidth, Tibbit #45 consumes an average current of 500mA, with peak current consumption of about 2A. While these current “spikes” are so narrow that they can’t be seen on a regular multimeter, they occur regularly when the modem is operating. We advise using an adequate power source to prevent unexpected reboots or unstable operation.

The modem consumes approximately 22mA when idle and sips about 1.6mA when in sleep mode. Note that the idle and sleep modes are not available when the Tibbit is in the automatic PPP connection mode.

The Tibbo Project System (TPS) platform offers several power supply Tibbits capable of providing sufficient current.

The TPS Online Configurator can help you decide which parts to use in conjunction with Tibbit #45. The Online Configurator lists the Tibbit as consuming 500mA of current, which we found to be a good approximation of the current burden it places on a power source, but does not take into account the current spikes or that the Tibbit often operates with lower power consumption.

Operating Temperature

In testing, this Tibbit operated normally in the –40°C to 85°C range. However, SIMCom recommends the –30°C to +80°C operating temperature range for its modem IC and warns of reduced performance when operating outside of this range.

In addition to the temperature constraints on the module, there are also limitations for off-the-shelf SIM cards. While regular consumer SIM cards are certified to operate in a temperature range of –25°C to +85°C, industrial/automotive SIM cards can operate from –40°C to +85°C, with some reaching even up to 105°C. In internal testing, some consumer SIM cards deformed at high and low temperatures. Therefore, we highly recommend that you asses your application's projected environmental conditions and choose and appropriate SIM card.

Library and AppBlocks Support

The CELL Library unlocks the full capabilities of this Tibbit. The library allows you to automate the process of initializing the modem and automatically establish and maintain a PPP connection. It also offers an AT command mode for manual control of the SIMcom modem.

This Tibbit is also supported in AppBlocks, Tibbo's in-browser, no-code, flowchart-based application development platform. You can access the platform at https://appblocks.io/.

The use of the library is illustrated by the following AppBlocks tutorial: https://appblocks.io/tutorials/4gswitchover.

Tibbit Variations

This Tibbit is supplied in three regional variants as detailed in Table 2.

1. While SIMCom identifies a few specific countries or regions for each variant of the SIM7500 family of modems, we have omitted them because they are not fully inclusive lists. What is important is that you select the version most compatible with the bands in use in your region (and compliant with your local regulations).