# Current Sense Resistor, Shunt Resistor

Here is a practical example of shunt resistor selection for an MPPT based solar charge controller circuit. The below circuit uses LT3652, an MPPT charge controller from Linear Technology (Analog devices). However, If we look carefully, the battery that will be charged through this circuit is the load.

The load is connected using a shunt resistor R6. The R6 will determine the charge current, which means the voltage drop of this R6 will remain constant in every case as V = I x R. The R will be constant, the V will be constant, the driver will change the charge current.

To select the shunt resistor, the following things will be required-

1. The constant voltage that will be used by the driver IC LT3652
2. The maximum charge current that is required to be delivered to the battery through the resistor.
3. Since it is a charge controller tolerance could be 1%.

As per the LT3652 datasheet, the sense pin will use 100 mV (0.1V) sense voltage that will be constant. Also, the maximum charge current LT3652 supports is 2A. Thus, the Shunt Resistor value needs to be R = V / I or Shunt resistor value will be 0.1V / 2A = 0.05 Ohms or 50 mili-ohms.

The power rating of this resistor needs to be P = I2R or P = 22 x 0.05 = 0.2 Watt. The close value of the shunt resistor will be 50 mili-ohms, 1% rated, 0.25 Watt. But instead of 0.25 Watt, 0.375 Watt is the safe resistor wattage that can be used.

Berikut fitur EagleCAD yang dapat digunakan:

# Set agar mata bor CNC berada pada titik Nol dengan ketinggian tepat diatas PCB

Brikut cara menset agar mata bor CNC berada pada titik Nol. Jika menggunakan software Mach3 maka cukup aktifkan CNC lalu pindah mata bor ke tempat yang diinginkan sebagai titik nol. Memindahkannya cukup menggunakan tombol panah kiri/kanan/atas/bawah pada keyboard. Tidak perlu mengiraukan ketinggiannya. Cukup sumbu X dan Y nya saja.

Ketinggian diatur dengan tombol PageUp dan PageDown. Pengturan harus hati hati agar tidak terlalu turun sehingga bor patah. Cukup di-tap (tekan sedikit demisedikit saja) jangan ditekan terus menerus. Jika sudah hampir menabrak media yang akan di-bor, maka hentikan pada kurang lebih ketinggian 10mm.

Pemasangan probe cukup mudah, namun butuh pengecekan dan mungkin pengaturan. Selanjutnya pasang probe yang biasanya dalan bentuk konektor jepit buaya. Jika tidak tersedia, bisa dibuat sendiri dengan munghubungkan panel probe-nya. Untuk meyakinkan bahwa probe berfungsi, maka buka bagian Diagnostics (Alt+F7) lalu tempelkan probe pada PCB. Jika pada pilihan Digitize berubah warna, maka probe telah berfungsi dengan baik. Namun jika belum berubah warna, coba cek bagian Config dan centang Probe dan Active Low.

Set semua menjadi titik Nol, biasanya cukup menekan tombol REFF ALL HOME, namun kadangkala ada sumbu X, Y, Z yang tidah mau berubah jadi 0. Maka tekan saja tombol tersebut. Selanjutnya buka file findzero.nc ini untuk memindah dan set ketinggian tepat diatas PCB.

```G0 Z0  (Pindah ke posisi 0,0,0)
G31 Z-10 F100 (Cari probe dengan arah Z negatif atau turun 10mm dengan kecepatan 100mm/det)
G92 Z0 (Jika probe telah ditemukan, maka set Z=0)
G0 Z2 (Pindah ke posisi Z=2 atau naik 2mm)
G31 Z-1 F50 (Cari probe lagi dengan kecepatan 50 mm/det)
G92 Z0 (Set ulang ketinggian menjadi 0)
G0 Z1 (Pindah ke posisi naik 1mm)
M1 (Pause atau berhenti sejenak)```

Selanjutnya tinggal lepas Probe dan CNC siap untuk digunakan.

# What do you have to know about MAX232

Max232 is designed by Maxim Integrated Products. This IC is widely used in RS232 Communication systems in which the conversion of voltage level is required to make TTL devices to be compatible with PC serial port and vice versa. This chip contains charge pumps which pumps the voltage to the Desired Level. It can be powered by a single +5 volt power supply and its output can reach +_7.5 volts.MAX232 comes in 16 Pin Dip and many other packages and it contains Dual Drivers. It can be used as a hardware layer convertor for 2 systems to communicate simultaneously.Max232 is one of the versatile IC to use in most of the signal voltage level conversion problems.

Construction of MAX232:

Mostly MAX232 used in 16-pin DIP package. it consist of 3 major blocks .It can only be powered by 5 volts to make it power supply compatible with most of the embedded systems. First block is the voltage doubler in this ic switched capacitor techniques is used to make the voltage double .Once the voltage is doubled second block will converts that voltage to +10 and -10. The third block consists of 2 transmitters and 2 receivers which actually convert the voltage levels.

External components:

Max232 requires minimum 4 external capacitor. Their Value can range from 1uf to 10uf and16 volts or more rating. There are many different versions of this versatile ic available each of them Require different capacitor value for proper working.

Application and uses of MAX232:

Premierly MAX232 is used in Serial communication. Problem arises when we have to communicate between TTL logic and CMOS logic based systems. RS232 is internationally defined standard named as EIA/TIA-232-E and in this standard logic 0 is the voltage between +3 to +15 and logic 1 is defined as the voltage between -3 to -15.In TTL logic 0 is defined is by 0 volt and 1 is defined by 5 volt so in this scenario this is a very handy IC to be incorporated.

Other Applications & Uses

• Battery Powered RS 232 Systems
• Interface Translation
• Low Power Modems
• RS 232 Networks (Multidrop)
• Portable Computing

PC Serial PORT communication by using MAX232 IC:

Desktop and some old Laptops have Serial port which comes in DB9 package. In Most of the Circuits designer is concerned about the Tx and Rx pins only so the function of the rest of the pins are not used here mostly.

In the above circuit only one Driver is used and second driver can be used for other purpose. TTL data is available on pin 12 and pin 11 and these pins can be attached to Microcontroller or any system which accept TTL logic.

GSM Modem Communication:

There are many GSM modems available in the market and most of them are on TTL logic but some of them use RS232 standards and again it becomes a problem to communicate wilt GSM modem by using Micro controller, aurdino or any other TTL platform.MAX232 is used to solve this problem.

Types of MAX232:

1)“MAX232N” where “N” Represent PDIP package Style this package is easy to sold and most widely used.

2) MAX232D where “D” indicates the SOIC package which is difficult to sold and required a trained professional to be used correctly.

#### Common mistakes:

• Capacitor voltage rating is less than 16.
• Interchange Tx and Rx pins on one side of MAX232 at one time.
• Distorted power supply. Use decoupling capacitor to remove distortion.
• Check all the connections again.
• Check the capacitor with capacitance meter.
• Use Tantalum Capacitor for better performance.

# Lensa Kontak Pintar Samsung dan Sony

Para insinyur Samsung sedang membangun sesuatu yang futuristik: lensa kontak pintar dilengkapi dengan tampilan serta sebuah kamera.

Meski masih dalam tahap awal pengembangan, eye-wear dimaksudkan untuk pemanfaatan augmented reality (AR) berpengalaman, dibandingkan dengan Google Glass dan teknologi lain yang dipakai. Alat yang telah dipatenkan di Korea Selatan ini memiliki layar khusus yang mengirimkan gambar langsung ke mata si pemakai.

Menurut keterangan yang diberikan oleh pengembang, lensa kontak dikendalikan oleh kedipan mata. Pengolahan data diproyeksikan ke layar pada perangkat eksternal, seperti smartphone.

Sementara itu, Sony tidak mau ketinggalan. Pera pengembang membuat lensa kontak yang memiliki memori yang dibenamkan pasa lensa kontak, sehingga penyimpanan data dapat langsung disimpan dalam lensa kontak tanpa membutuhkan piranti eksternal.

Lensa kontak besutan Sony dilengkapi dengan sensor piezoelektrik mini yang mampu mengenali perubahan tekanan, temperatur, akselerasi dan daya. Sensor pada kemudian mengkonversi perubahan ini menjadi muatan listrik, yang kemudian akan digunakan untuk mengaktifkan rekaman melelui gerakan mata pemakainya.

Sumber:

# Perlindungan kesalahan pemasangan baterai dengan FET

Perangkat elektronik banyak digunakan pada saat ini, bahakan setiap satu orang bisa memiliki tiga sampai lima perangkat elektronik. Perangkat elektronik portabel memerlukan catudaya berupa baterai untuk dapat tetap bekerja. Namun bagaimana jika pengguna alat elektronik salah memasang baterai secara terbalik? Hal tersebut dapat merusak IC atau perangkat sensitif lainnya. Dalam beberapa perangkat telah dipasangkan perlindungan kesalahan pemasangan baterai.
Cara termudah untuk proteksi baterai adalah dengan memasangkan dioda secara seri dengan baterai. Dioda mampu menapis arus dari arah berlawanan (reverse current), namun memiliki kekurangan pada turunnya tengangan pada arus maju (forward bias) kurang lebih 0,6 Volt.
FET (Field Effect Transistor) kini memiliki hambatan aktif (on-resistance) yang sangat kecil, sehingga dapat diaplikasikan sebagai proteksi perlindungan pemasangan baterai.
Sumber: http://www.ti.com/lit/an/slva139/slva139.pdf

# IC Catu daya terkecil dan simpel

Produsen IC Maxim Integrated menawarkan produk baru mereka untuk solusi catu daya dengan mengeluarkan produk MAX1722/MAX1723/MAX1724 yang mereka namai dengan Small Low-Power Boost Converter.
Beberapa keunggulannya antara lain adalah kemampuan untuk mengubah tegangag catu daya daro 0.8 volt menjadi 3,3 Volt (cukup untuk tegangan IC TTL) dengan hanya menambahkan komponen induktor dan kapasitor agar IC tersebut dapat bekerja. IC hanya membutuhkan catu daya 1,5 mikro Ampere, sehingga disinyalir mampu menghemat daya baterai, terutama untuk diterapkan di perangkat mobile. Sayangnya, hasil dari catu daya IC dengan bentuk paket TSOT ini masih sebatas 150 mili Ampere saja.

Sumber:

• http://monitor.espec.ws/section27/printview200427.html
• http://monitor.espec.ws/section27/printview200427.html

# Bypass Capacitors – Why and How to Use Them?

You may have heard about the phenomenon of bypassing in circuits, however, we may not have sufficient knowledge of how to apply this technique in real circuits. In this tutorial, we will discuss about the bypass capacitors, why we need to use and how to use these capacitors in circuits.

## What is a Bypass Capacitor?

A capacitor that filters out the AC signal removing the noise and provides a DC signal is known as a bypass capacitor. The capacitor connected in the figure below is a bypass capacitor bypassing AC noise and allowing pure DC signal to pass through the component.

Operation of a Bypass Capacitor

## Why Use Bypass Capacitors?

In electronics, most of the circuits are digital in nature using direct current (DC). It has been observed that variations in voltage can cause problems to the circuit operation. A circuit may operate incorrectly due to voltage swing. In practical circuits, the voltage fluctuation is usually caused by the AC component that may ride over DC signal causing noise. Therefore, a bypass capacitor is needed to dampen the AC or noise present at all frequencies. Also, it prevents the unwanted communication between devices sharing the same power source.

## When do you Need Bypass Capacitors?

Firstly, the low frequency circuits may not require bypass capacitors. However, many low frequency active devices comprise of high frequency units. For example, a microcontroller is a low frequency device using a clock making a low frequency system, but the rising and falling glitches can occur due to internal gate transitions without proper filtering of power supply that will traverse the circuit. Therefore, you may need a bypass capacitor with an appropriate value to achieve proper filtering of power supply.

Secondly, you may have this misconception that only digital devices need bypass capacitors. However, bypass capacitors also benefit the analog circuits and devices in a different way. In digital systems, bypass capacitors control the fast timing of rising and falling glitches. Conversely, bypass capacitors help in reducing noise of power supply in analog systems. Generally, analog devices have built in capability of filtering power supply that is effective for reducing low frequency power supply noise, but it is not useful at higher frequencies.

## Types of Bypass Capacitor

Bypass capacitors are usually used in high speed environments where the capacitor inductances play a very critical role. The output of a part generates high frequency noise, typically greater than 100 MHz, on the power line at high speed switching. A high lead inductance capacitor will behave as an open circuit due to these harmonics which prevents it from providing the needed current to the power line to maintain a stable level, which results in failure of circuit functionality. Therefore, capacitors with very small inductances are required to bypass the internal noise of the device.

The inductance of a typical surface mount ceramic capacitor is 0.5nH, while the inductance of an electrolytic capacitor is 15nH. By calculating the inductive impedance of these bypass capacitors, we can observe the effect on bypassing:

Electrolytic Capacitor Ceramic Capacitor
$Z_L = 2 pi fL$
$Z_L = 2 x 3.142x 1.5x10^{8}x 15x10^{-9}$
$Z_L = 14 Omega$
$Z_L = 2 pi fL$
$Z_L = 2x 3.142x1.5x10^{8}x 0.5x10^{-9}$
$Z_L = 0.4 Omega$
$V_{drop} = IxZ_L$
$V_{drop} = (0.04 A)x (14 Omega)$
$V_{drop} = 0.56V$
$V_{drop} = IxZ_L$
$V_{drop} = (0.04 A)x (0.4 Omega)$
$V_{drop} = 0.016V$

From this example, we have observed that supply voltage drops below the operating voltage of the device due to more than one channel switching at the same time. Therefore, it is important to use the correct type of bypass capacitor. This is the reason that ceramic capacitors are more favorable than electrolytic capacitors for bypassing. They allow easy flow of charge when needed due to negligible internal inductance.

## How to Select Value of Bypass Capacitor?

Now we know why and when we need to use bypass capacitors, but we still need to find out the appropriate value of the capacitor to use for a particular device. The typical values considered for bypass capacitors are 0.1 µF and 1 µF. The higher the frequency, the smaller the value; while the lower the frequency, the large the value.

$f = frac{1}{2t_R}$

where tR = rise time.

The most important parameter to select an appropriate bypass capacitor is its ability to supply instantaneous current when it is needed. In order to select the capacitor size for a particular device, we have the following methods:

1. Firstly, the bypass capacitor size can be calculated using the following equation:

$C = frac{I*N* Delta t}{Delta V}$

I = amount of current needed to switch one output from low to high

N = switching number of outputs

∆t = time required to charge the line by the capacitor

∆V = tolerated drop in VCC

The values given in the formula should be known, where ∆t and ∆V can be assumed.

2. Another way to find out the bypass capacitor size is by calculating its maximum current with the specified maximum pulse slew rate. Maximum pulse slew rate is specified by several capacitor manufacturers.

$I = Cfrac{dV}{dt}$

## How to Use Bypass Capacitors?

The bypass capacitor value depends on the noise frequency of the supply that requires filtering. Therefore, a typical bypass capacitor of 0.01 µF or 0.1 µF is connected for high frequency supply noise and low current applications as shown in figure below:

Bypass capacitor for low current and high frequency application

However, power supply lines may have multiple frequencies in some applications where a single bypass capacitor is not sufficient. Thus, a network of bypass capacitors is used to filter the noise of wider range of frequencies. An example is given in the circuit below where capacitor C2 filters mid range frequencies, C3 filters higher frequencies and C4 filters low frequencies.

Bypass capacitor network for filtering multiple frequencies

It is also important to know that the bypass capacitors should be connected closer to the power supply pins because longer traces on printed circuit boards will increase the inductance and lower the frequency of the bypass track.

## Example of a Bypass Capacitor Application

It is simple and easy to use a bypass capacitor in a circuit without changing the connections of other circuit components. A bypass capacitor is simply placed between power source (VCC) and ground of each active device, as shown in figure below:

Bypass Capacitor connected in a Circuit

In the given circuit, the bypass capacitor is responsible for holding the emitter voltage steady and maintaining voltage gain. For the transistor connected in the above given circuit, iC increases as iB rises, increasing the emitter voltage. This decreases VBE that decreases iC resisting the rise in emitter voltage. Here the bypass capacitor is connected to shunt the signal occurring at the emitter through to the ground.