Linx

How to Use the LC Series LINX Modules

by Lee Rumsey

These are basic instructions on hooking up the modules. This document is split into five nifty sections:

For data sheets on the LINX modules, see this web site: http://www.linxtechnologies.com. Click on the RF Modules link. Then click on the Manuals item under the LC Series heading. READ through the LC Series data sheets to get an understanding of their function. This will reduce the likelihood of errors.

Necessary Parts

TX board (1) Smaller PC board; has TXM-XXX-LC chip on it
RX board (1) Larger PC board; has RXM-XXX-LC chip on it
Antenna (2) Either whips or helical antennas
RG-174 50W coax cable Available from ECE Store; for connecting antennas
22 ga hookup wire Should be laying around the 445 lab
390 W, 1/4 W resistor (1) Needed for 5V operation

Before we start

  1. Learn to solder. You will be making some delicate connections, so practice if you don't know how. Also be sure to use solder sparingly- big blobs will likely result in damage or malfunctions.
  2. You should have the parts listed above. Get them from a TA.
  3. Make sure the transmitter and receiver are running on the same frequency. Do this by checking the model number on the surface mount package. For example, a 418 MHz TX module will be labeled TXM-418-LC, and a 315 MHz RX module will be RXM-315-LC.

Transmitter Assembly

The LINX transmitter is the smaller of the two modules. It runs on between +2.7 and 5.2 VDC. We will use a +5 VDC power supply, so that the data input can be a TTL level signal. DO NOT apply a voltage greater than Vcc on the data input pin!

Step 1. Acclimate yourself with the circuit we are building:
schematic

Step 2. Place the TX board with chip side facing UP. The writing on the chip should be right side up, with a little wire coming off the top. This wire is GROUND. A '1' or a small dot should be visible on the lower left-hand corner of the chip. GROUND is also connected to the center bus strip on the board.

Step 3. Solder the 390 W resistor from pin 4 (lower right-hand corner) to ground. This sets the chip to accept 5 VDC. NOTE: make all connections on the top of the board. DON'T feed any leads through the holes. There are connections on the other side!

Step 4. Carefully solder a 3-inch wire to pin 2. This will be the DATA input. DO NOT apply a voltage greater than Vcc on the data input pin!

Step 5. Carefully solder a 3-inch wire to pin 7. This will be the VCC power input. REMEMBER: +5 VDC ONLY on this pin!

Step 6a. If you have a HELICAL COIL antenna, solder a short (2 inch) length of coax cable to pin 5 and GROUND. The inner conductor is the RF signal, and the outer shield goes to GROUND. Now solder the helical coil to the other end of the coax to form a magnetic loop. (You may need to extend the shield connection with a separate wire.)

Step 6b. If you have a WHIP antenna, solder the coax cable directly to pin 5 and GROUND. The inner conductor is the RF signal, and the outer shield goes to GROUND.

Here is the completed TX board assembly:
board


Receiver Assembly

The LINX receiver is the larger of the two modules. It runs on between +4 and 5.2 VDC. We will use a +5 VDC power supply. GROUND is the center vertical strip on the solder side.

Step 1. Acclimate yourself with the circuit we are building:
circuit

Step 2. Place the RX board with chip side facing DOWN, with the solder side UP. Orient the board so that one wire comes off the top, while another comes off the left of the board. The top wire is the power connection; the left wire is ground. Pin 1 of the chip is actually at the lower left with this orientation; it is identified on the chip by a '1' or a dot.

Step 3. Carefully solder a 3-inch wire to pin 5 (top left solder pad connected to the chip). This will be the DATA output.

Step 4a. If you have a HELICAL COIL antenna, solder a short (2 inch) length of coax cable to pin 1 and GROUND. The inner conductor is the RF signal, and the outer shield goes to GROUND. Now solder the helical coil to the other end of the coax to form a magnetic loop. (You may need to extend the shield connection with a separate wire.)

Step 4b. If you have a WHIP antenna, solder the coax cable directly to pin 1 and GROUND. The inner conductor is the RF signal, and the outer shield goes to GROUND.

Step 5. IMPORTANT! If there is a connection to pin 10 on the Linx chip, carefully desolder it, leaving the others intact. It is misconnected.

Here is the completed RX board assembly:
complete


Testing and Operation

Now we'll see if these modules work. If you are working with 418 MHz chips, then a reference receiver - transmitter pair are available for testing. Otherwise, you better hope you made the right connections? we don't have anything to test the 315 MHz RX/TX chips, except maybe another functioning pair of modules.

Step 1. TESTING THE TRANSMITTER. Refer to the schematic for the TX module we just assembled. Connect +5 VDC to the power lead, and ground the GROUND lead.

Step 2. Turn on or plug in the power. Use +5 VDC only! If anything is heating up, UNPLUG the module and check your connections!

Step 3. Set up a function generator the make a 1 kHz TTL compatible square wave (i.e. it swings between 0 and +5V only!) Connect this signal to the data input lead from the module. If anything is heating up, UNPLUG the module and check your connections!

Step 4. Plug the data output of the reference receiver into an oscilloscope. ASK A TA FOR ASSISTANCE! If all is well, a 1 kHz square wave should appear on the screen. You are done; wire your module into the rest of your circuit.

NOTE: For a flaky power supply, a bypass capacitor (10 uF electrolytic) may be necessary between power and ground on YOUR board.

Step 5. TESTING THE RECEIVER. Refer to the schematic for the RX module we just assembled. Connect +5 VDC to the power lead, and ground the GROUND lead

Step 6. Turn on or plug in the power. Use +5 VDC only! If anything is heating up, UNPLUG the module and check your connections!

Step 7. Set up a function generator the make a 1 kHz TTL compatible square wave (i.e. it swings between 0 and +5V only!) Connect this signal to the data input on the reference transmitter. ASK A TA FOR ASSISTANCE! If anything is heating up, UNPLUG the module and check your connections!

Step 8. Connect the data output of your receiver module into an oscilloscope. If all is well, a 1 kHz square wave should appear on the screen. You are done; wire your module into the rest of your circuit.

THE END.

Modularized Electronic Locker

Jack Davis, Joshua Nolan, Jake Pu

Modularized Electronic Locker

Featured Project

Group Member: Jianhao (Jake) Pu [jpu3], Joshua Nolan [jtnolan2], John (Jack) Davis [johnhd4]

Problem:

Students living off campus without a packaging station are affected by stolen packages all the time. As a result of privacy concerns and inconsistent deployment, public cameras in Champaign and around the world cannot always be relied upon. Therefore, it can be very difficult for victims to gather evidence for a police report. Most of the time, the value of stolen items is small and they are usually compensated by the sellers (Amazon and Apple are very understanding). However, not all deliveries are insured and many people are suffering from stolen food deliveries during the COVID-19 crisis. We need a low-cost solution that can protect deliveries from all vendors.

Solution Overview:

Our solution is similar to Amazon Hub Apartment Locker and Luxer One. Like these services, our product will securely enclose the package until the owners claim the contents inside. The owner of the contents can claim it using a phone number or a unique user identification code generated and managed by a cloud service.

The first difference we want to make from these competitors is cost. According to an article, the cost of a single locker is from $6000 - $20000. We want to minimize such costs so that we can replace the traditional mailbox. We talked to a Chinese manufacturer and got a hardware quote of $3000. We can squeeze this cost if we just design our own control module on ESP32 microcontrollers.

The second difference we want to make is modularity. We will have a sensor module, a control module, a power module and any number of storage units for hardware. We want to make standardized storage units that can be stacked into any configuration, and these storage units can be connected to a control module through a communication bus. The control module houses the hardware to open or close all of the individual lockers. A household can purchase a single locker and a control module just for one family while apartment buildings can stack them into the lockers we see at Amazon Hub. I think the hardware connection will be a challenge but it will be very effective at lowering the cost once we can massively manufacture these unit lockers.

Solution Components:

Storage Unit

Basic units that provide a locker feature. Each storage unit will have a cheap microcontroller to work as a slave on the communication bus and control its electronic lock (12V 36W). It has four connectors on top, bottom, left, and right sides for stackable configuration.

Control Unit

Should have the same dimension as one of the storage units so that it could be stacked with them. Houses ESP32 microcontroller to run control logics on all storage units and uses the built-in WiFi to upload data to a cloud server. If sensor units are detected, it should activate more security features accordingly.

Power Unit

Power from the wall or from a backup battery power supply and the associated controls to deliver power to the system. Able to sustain high current in a short time (36W for each electronic lock). It should also have protection against overvoltage and overcurrent.

Sensor Modules

Sensors such as cameras, motion sensors, and gyroscopes will parlay any scandalous activities to the control unit and will be able to capture a photo to report to authorities. Sensors will also have modularity for increased security capabilities.

Cloud Support

Runs a database that keeps user identification information and the security images. Pushes notification to end-users.

Criterion for Success:

Deliverers (Fedex, Amazon, Uber Eats, etc.) are able to open the locker using a touchscreen and a use- provided code to place their package inside. Once the package is inside of the locker, a message will be sent to the locker owner that their delivery has arrived. Locker owners are able to open the locker using a touchscreen interface. Owners are also able to change the passcode at any time for security reasons. The locker must be difficult to break into and offer theft protection after multiple incorrect password attempts.

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