[Photo] Using MEC002A to make a remote FM transmitter

Author: Lin Changhao

This article introduces several remote FM mono and stereo transmitters made with the miniature and efficient wireless sound transmission module MEC002A. Because the core device MEC002A used has the advantages of perfect function, wide operating voltage range, high transmission efficiency, long range, etc., the FM transmitter formed by it is easy to manufacture and simple to debug. The external size of MEC002A is 16x16x22mm, pin arrangement The standard pitch 7-pin single-in-line type is used. Its external dimensions and function of each pin are shown in Figure 1, and its internal structure is shown in Figure 2. The module itself contains a microphone and an audio amplifier circuit. The sound hole is completely exposed on the top surface of the module, which can fully receive sounds in all directions, and the sound sensitivity is quite high. Its sound sensing sensitivity can also be controlled by an external resistor R; the module is used Basically, there is no need to connect any components, as long as the power is turned on to work.

1. The simplest remote FM transmitter:

The simplest remote FM transmitter circuit is shown in Figure 3. Because the module has a large RF output power, connect the circuit according to Figure 3 and turn on the power to transmit. When the operating voltage is 12V, the transmitting antenna uses 1.5 meters The whip antenna has a transmission distance of nearly 1,000 kilometers in an open area. To adjust the sound transmission sensitivity, you can change the resistance of the resistance between the AI ​​and AO pins. The smaller the resistance, the higher the sound transmission sensitivity, and vice versa. It is generally controlled at 500Ω-10KΩ, and its minimum resistance is generally not less than 500Ω, otherwise it may affect the normal operation of the module. By applying this circuit, it can be made into FM wireless microphone, wireless intercom, monitor for anti-theft alarm, monitor for hospital ward, etc. If you want to make the internal microphone not work and need to use external audio signal for modulation, you can disconnect the G1 and GND short contacts and AI and AO short contacts on the soldering board. The external audio signal is sent to the AI ​​pin from the socket. The circuit can also be used to make a remote control transmitter with data transmission function. The circuit can be connected with reference to the dotted line in Figure 3. The data input terminal DATA_IN can be connected to the coded data output terminal of data coding integration (such as VD5026, etc.).

What is the working voltage, current and reference emission distance of MEC002A?

2. Remote FM transmitter with power extension:

Old board new board

The actual transmission distance of the FM transmitter shown in Figure 3 is about 300-500 meters in the area with houses and other buildings. When it is used as a small-area FM transmitter station (such as campus radio, etc.), the transmission distance generally requires 1-3 kilometers. It is necessary to further increase the RF output power of the transmitter. Because the RF output power of MEC002A is large, it can directly excite the Class C RF power amplifier circuit, and the working efficiency of the Class C RF power amplifier circuit is higher, so only one more level needs to be added. The C-type RF power amplifier circuit composed of C1971 can effectively increase its transmission distance to 1-3 kilometers. The power expansion circuit of MEC002A is shown in FIG. 4, and its RF signal is transmitted by the coupling circuit to the base of the high-frequency power tube C1971. The amplified RF signal is filtered and emitted by the antenna into the air. The input and output coupling circuit of the Class C RF power amplifier circuit in Fig. 4 resonates at 79MHz. The MEC002A model should use a center frequency of about 79MHz and 2MHz, such as MEC002A12V80MHz. , The transmitting antenna can use the whip antenna of 1.2-1.5 meters or outdoor antenna, when using outdoor antenna When shooting from its role in the open area up to three kilometers. This circuit uses only two-stage circuits to achieve a transmission distance of one kilometer, making it very easy to make this remote FM transmitter. Generally, as long as the assembly is completed, it is only necessary to fine-tune the input-output coupling circuit to resonate at the center frequency of the sound transmission module. The entire circuit consumes about 300mA, and the power supply is preferably made up of 3 motorcycles with 6V batteries connected in series. If you use commercial power supply, you must make sure the voltage regulator and filter circuit, otherwise it will introduce hum interference and even cause the entire circuit to fail normal work.

3. Remote FM stereo transmitter:

Old board new board

Figure 5 is based on Figure 4 by adding a level of FM stereo coding circuit composed of BA1404, so that Figure 4 is upgraded from a mono transmitter to a mono, stereo dual-purpose FM transmitter, here the BA1404 is abandoned The front audio amplifier circuit, RF oscillation circuit and RF power amplifier circuit are not used, only the internal stereo encoding part of the circuit is used. The 19KHz pilot signal and stereo composite signal are output by pins 13 and 14 of BA1404 and sent to MEC002A Modulation port AI adjusts the frequency of the internal high-frequency oscillation source of the module. This machine is very suitable for FM stereo broadcasting station used in schools or units.

The above introduces several FM transmitters with a transmission distance of less than 3 kilometers. If you want to further increase the transmission power, you can add an additional RF buffer amplifier circuit composed of C2053 between MEC002A and C1971 to improve the radio frequency of C1971. Excitation power, so that the transmission distance is increased to 3-5 kilometers, the input and output coupling circuit of the buffer amplifier circuit is basically similar to the C1971 level, the reader can design it by himself, no more details here, the working current of the entire circuit is controlled at about 500-800mA .

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PCB SMT Stencil ,the unique goal  is to move solder paste to the bare Printed Circuit Board.

PCB Stencil , SMT Stencil, SMD Stencil , Laser Stencil , What is it?

Apart from all types of Printed Circuit Boards (PCBs) such as Prototype PCB , Aluminum PCB , HDI PCB , Flexible PCB , Rigid Flex PCB , Thick Copper PCB, High TG PCB , JHYPCB also manufactures solder paste stencils to meet Surface Mount Technology (SMT) requirements.

PCB Stencils, also called SMT stencils, SMD stencil, play a key role in transferring accurate amount of solder paste to correct positions on bare circuit boards ready for assembly. In other words, stencils can fast and efficiently ensure the most accurate solder paste amount and optimal electrical connection. With solder stencils, it is possible to use metal squeegee blades to apply solder paste easily over the openings on PCBs and make stencil to be well aligned with the surface of the advanced circuit board.

All of our SMT Stencils stencils are 100% laser-cut type 304 full-hard stainless steel, ensuring the finest quality finish on the market today. We use a .001" laser beam with 98% overlap creating an extremely smooth hole that provides the best paste release. Most stencil fabricators use a .003" laser leaving mouse bites on the aperture edge. You can choose a PCB Prototype stencil, a frameless foil stencil, or a rigid permanently mounted stencil. Both the frameless and framed stencils come in various sizes to accommodate your printer and stencil requirements.

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PCB Stencil Types Available:

1. Laser-cut stencils

The openings are lasered on 100% stainless steel. Generally speaking, this kind of stencil can be produced with high quality and a high degree of precision within a short time.

• Advantages: high accuracy; barely influenced by objective elements; trapezoid opening beneficial for demoulding; suitable for accurate cutting; reasonable price;

• Disadvantages: relative low manufacturing speed.

2. Chemical-etch stencil

The openings are etched into the metal using acid. Usually this kind of stencil offers better protection on material temper and hardness.

• Advantages: one-time formation; relatively high manufacturing speed; low cost;

• Disadvantages: tending to form sand clock shape or large openings; numerous manufacturing stages and accumulating errors; unsuitable for fine pitch stencils; bad for environmental protection.

3. Prototype PCB Stencil (Low-volume manual printing. Ideal for prototypes)

When prototyping dictates fast action with minimal cost, our prototype stencils are the best solution. Prototype Stencils gives you a quality stencil and framework so you can handle assembly from the convenience of your own desk.

Prototype SMT Stencil Features:

• Eliminate the registration difficulty associated in hand printing with a flat piece of metal
• Eliminate printer set up for short run prototypes
• Allow quick alignment for repeatability
• Save money over full size stencils designed for automated printers<
• Squeegee included

Prototype SMT Stencil Specs:
Technology	100% laser cut
Material Used	Stainless Steel
Stencil Thickness	0.06 ~ 0.3 mm
Minimum Cut Width	0.05 mm
Maximum Size	736 X736 mm
Aperture Tolerance	within 0.007mm
Allow for Fiducial Data	Yes
Delivery	1 ~2 Day

4. NEW Prototype PCB Stencil Kit (with leaded or lead/free solderpaste)

Includes Prototype Stencil, one board holder, leaded or lead-free solder paste (must specify), temperature marker, squeegee, ESK-safe gloves and alcohol wipe. 

5. NEW Pick and Place Tool

Handy and convenient for low quantity prototype assembly using the Prototype Stencils.  Re-usable, includes vacuum bulb and vacuum clips with diameters of 3/8", 1/4", and 1/8".

6. Framed SMT Stencils (Also called "Glue-in" or Mounted Stencils)

Framed stencils are laser-cut stencils designed for high volume screen-printing. With a framed stencil, your stencil is securely mounted to either a cast or extruded aluminum stencil frame a stencil frame using a mesh border, allowing for complete control.

Framed SMT Stencil Features:

• Unique Process for smooth aperture walls
• Very clean laser-cut apertures
• Excellent print performance
• Excellent for high-volume stencil printing on printed circuit boards
• Unique process creates permanent non-removable non-fading fiducial
• All framed SMT stencils are double bonded to extreme wear
• 24-hour turnaround standard

Framed SMT Stencil Specs:
Technology	100% laser cut
Material Used	Stainless Steel
Frame Types	Cast, Space Saver
Stencil Thickness	0.06 ~ 0.3 mm
Minimum Cut Width	0.05 mm
Maximum Size	736 X736 mm
Aperture Tolerance	within 0.007mm
Allow for Fiducial Data	Yes
Allow for Panelized Data	Yes
Delivery	1 ~2 Day

Framed PCB Stencil Specification

Framed PCB Stencil Area	Maximum Squeegee Area
300mm*400mm (11.81inch*15.75inch)	120mm*220mm (4.72inch*8.66inch)
370mm*470mm (14.57inch*18.5inch)	200mm*300mm (7.87inch*11.81inch)
400mm*600mm (15.75inch*23.62inch)	220mm*400mm (8.66inch*15.75inch)
400mm*700mm (15.75inch*27.56inch)	220mm*500mm (8.66inch*19.69inch)
400mm*800mm (15.75inch*31.5inch)	220mm*600mm (8.66inch*23.62inch)
400mm*900mm (15.75inch*35.43inch)	220mm*700mm (8.66inch*27.56inch)
400mm*1000mm (15.75inch*39.37inch)	220mm*800mm (8.66inch*31.5inch)
400mm*1200mm (15.75inch*47.24inch)	220mm*1000mm (8.66inch*39.37inch)
400mm*1400mm (15.75inch*55.12inch)	220mm*1200mm (8.66inch*47.24inch)
420mm*520mm (16.54inch*20.47inch)	240mm*340mm (9.45inch*13.39inch)
450mm*550mm (17.72inch*21.65inch)	270mm*370mm (10.63inch*14.57inch)
500mm*800mm (19.69inch*31.5inch)	320mm*600mm (12.6inch*23.62inch)
500mm*1200mm (19.69inch*47.24inch)	320mm*1000mm (12.6inch*39.37inch)
550mm*650mm (21.65inch*25.59inch)	340mm*440mm (13.39inch*17.32inch)
584mm*584mm  (23inch*23inch)	380mm*380mm (15inch*15inch)
736mm*736mm (29inch*29inch)	480mm*480mm (19inch*19inch)

7. Frameless SMT Stencil - Foil/Plate Only (for universal frames)

Foil or Plate Only stencils are designed to work within interchangeable plate or "universal" systems. Also referred to as "reusable", these stencils do not need to be permanently glued into a frame.

Frameless SMT Stencils also referred to as foils are laser cut solder paste stencils designed to work with stencil tensioning systems known as reusable stencil frames. This type of stencil does not need to be permanently glued in a frame. Frameless stencils are significantly less expensive than framed stencils and provide money-saving storage while still delivering superior quality and performance.

Frameless SMT Stencil Features:

• Reduced storage space requirements
• Significantly less expensive than framed stencils
• Excellent for prototype Printed Circuit Board Assembly or short runs
• Smooth aperture walls, can be used for 16 Mil pitch and below and for Micro BGA's
• 24-hour turnaround standard

Frameless SMT Stencil Specs:
Technology	100% laser cut
Material Used	Stainless Steel
Stencil Thickness	0.06 ~ 0.3 mm
Minimum Cut Width	0.05 mm
Maximum Size	280 X 380 mm
Allow for Fiducial Data	Yes
Allow for Panelized Data	Yes
Delivery	1 ~2 Day

8. Frameless SMT Stencil - Foil/Plate Only (for hand printing)

For times when you need precise control for smaller production runs, our Foil or Plate Only stencils are ideal. These frameless stencils allow you to hand print with precision just the amount you need and can be stored conveniently.

9. Electroformed SMT Stencils

Electroformed SMT stencils are nickel-based, electroform foils permanently mounted in a stencil frame using a mesh border to tightly stretch the stencil foil taut in the frame. Electroformed stencils offer the best paste release characteristics available and are frequently used for fine pitch (20 mil to 12 mil pitch) SMT applications on printed circuit boards. They are also used for µBGA's, Flip Chip, and Wafer Bumping (12 mil to 6 mil pitch).

Electroformed SMT Stencil Features:

• The smooth trapezoidal sidewalls of an electroformed stencil allow for better paste release
• Nickel has a lower coefficient of friction compared to stainless steel
• Electroform foils are harder than full hard stainless steel of comparable thickness, providing for longer stencil life
• 24-hour turnaround standard

Electroformed SMT Stencil Specs:
Technology	Electroforming
Material Used	Nickel
Suitable Applications	All Component Pitches
Aperture Tolerance	within 0.007mm
Stencil Thickness	0.06 ~ 0.3 mm
	0.06mm.0.08mm.0.1mm.0.12mm.0.13mm.0.15mm.0.18mm.0.2mm.0.3mm
Positional Accuracy	± 0.008mm
Delivery	1 ~2 Day

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What's the difference between a framed stencil and a frameless stencil?

A framed PCB stencil will have a 0.5" to 1.5" thick metal frame around it, similar to a picture frame. Framed stencils are often used by contract manufacturers, assembly and board houses, and large scale production facilities and are commonly placed in a manual or automated stencil printing machine. Frameless stencils are a thin sheet of material cut with a small border around your design. For example pictures on these products, please visit our Gallery.

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What's the difference between Polyimide and Stainless Steel?

All stencils are made with high quality Polyimide and Stainless Steel. We use only the industry leading Stainless Steel, designed specifically for stencils. These materials are ideal for prototype or Multilayer PCB .

Stainless Steel: 0.0007" Laser spot size, 0.001" minimum aperature size.
Polyimide Film: 0.003" Laser spot size, 0.005" minimum aperature size.

Polyimide has a lower precision rate due to the way it is processed and its ability to withstand heat during the cutting process. Minor variances will occur when the material reacts to the laser. Paste release is great, but this material should be limited to a small number of uses and with components 0402 or bigger.

The minimum aperature size for Polyimide is 0.005" vs 0.001" for Stainless Steel. Polyimide also has a natural curl in the material caused by the way the film is manufacturered, this is outside of our control. Stainless Steel provides the ultimate in precision and quality, with a 0.0007" spot size, and exceptional paste release with a truly flat surface. If you want the absolute best reflow experience, there is no comparison, Stainless Steel is the superior material.

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Analysis and Treatment of Common Problems in PCB SMT stencil

• Insufficient solder paste

Insufficient solder paste may cause poor bonds and contact between components and the board. The common causes of insufficient solder paste are poor gasketing, clogged stencil apertures, insufficient solder paste bead size, paste/stencil being used beyond recommended life span, stencil not wiped clean, or low squeegee pressure.

• Smudging/bridging

The main causes of smudging/bridging are excessive squeegee pressure, inadequate stencil wiping, poor contact between the board and stencil, high temperature or humidity, or low solder paste viscosity.

• Misalignment print

A typical misalignment print is usually caused by the vision system not spotting fiducials, PWB or stencil stretch, poor contact between the board and the stencil, or weak board support.

• Bow and twist

A PCB Board not fixed properly during solder paste printing gives poor results and increases soldering related issues. Normally, solder paste printing equipment can handle warpage of 1.0 to 3.0 mm but beyond this limit needs some special jigs or fixtures to hold the PCB. It may be difficult to tackle thick and small boards compared to thin and bigger size boards.

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How to Determine Stencil Size?

Stencil size is composed by two parts: internal size and overall size. Internal size is the size compatible with that of PCB ready to be assembled while overall size refers to the size compatible with printer parameter limit. As long as both sizes are accurately designed, stencil will be able to make full use of its functions.

Internal size of stencil can be figured out conforming to the following rule:

• Width of Framed Stencil = width of PCB + 100mm while its Length = length of PCB + 100mm
• Width of Frameless stencil = width of PCB + 200mm while its Length = length of PCB + 200mm

For example, if one circuit board size is 50*50mm, then the size of its framed stencil should be around 150*150mm and the size of its frameless stencil should be around 250*250 mm.

It's easy to remember and operate so it worked for manual solder paste printing in SMT assembly prior to the advent of automatic printer. It can be said that different PCB sizes lead to generations of different internal sizes of stencil.

When it comes to automatic solder paste printer, however, it's relatively solid. Overall size of stencil has to be determined by parameter limit of the equipment, that is, printer, because stencil has to work within the range of printer with a frame. Different printers feature different parameter regulations. As far as PCBCart is concerned, the stencil size compatible with our printer can be either 650mm*650mm or 736mm*736mm.

PCB designers have to focus on internal size of stencil, they don't need to care about its overall size since it is generally determined by the parameters of printer in your contract assembler workshop.

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How to Use PCB SMT Stencils?

PCB Stencil

PCB Stencil,SMT Stencil,SMD Stencil,Laser Stencil

JingHongYi PCB (HK) Co., Limited , https://www.pcbjhy.com