Since we want the voltage appearing at the IC to be equivalent to one cell, we first must “divide” the cell voltage by the number of cells in the pack. The ladder resistors R2 -R24 form an effective voltage divider circuit so that the BAT (pin 7) voltage will be about 1.25 V per cell. The switch can increase or decrease the BAT voltage by adding or subtracting “rungs” from the voltage divider ladder. Another divider network consists of resistors R14 and R16. This voltage sets up the MCV voltage for the BQ2003 IC. This should measure 1.8 V when in operation.

Seeing how you’ll want to charge your batteries quickly, you need a high charging current power supply to back you up. Transistors Q2, Q1, and components D1 and L1 form the “high current” portion of our “switched- mode-regulator” circuit. When the MOD output goes “high”, transistor Q2 is turned on, like a switch. This current then flows into the battery. Resistor R29 (and/or R27) is in series with the current flow and the voltage drop across it is sensed by IC pin 9, the sense pin. When the sense pin reaches its trigger point, the transistor is abruptly turned off. When this occurs, the magnetic field around the coil quickly collapses and causes a reverse voltage “spike” which is routed through the “catch” diode D1. This energy is recovered and delivered to the battery cells being charged. This is what provides us with the high current to quickly charge the cell, but does not dissipate power in the FET or NPN transistor, making the switched power much more efficient than a conventional pass transistor type of supply. Another contributing factor to the charging circuit is the charge rate setup, which is configured using resistors R26 and 27, as well as test points A - F.

Transistor Q3 is the integral part of our constant current discharging circuit. When the chip sees a positive going pulse at the DCMD pin, it initiates the DIS discharge output. With switch S1:10 closed diodes D2 and D4 are forward biased, causing 1.4VDC to be present at the base of Q3. With 1.4 V at the base, there is .7 VDC at the emitter, a diode drop in potential lost through the transistor. With the emitter at .7 VDC, the current through resistors R10 and R22 is about 140 mA, regardless of the cell voltages. If switch S1:10 is opened the potential increases to 1.4 VDC. increasing the current to 280 mA. This will continue to discharge the batteries until they reach a potential of about .9 volts per cell. The Benchmarq chip then initiates its own charging sequence.

A few final points concerning the TM1 and TM2 time-out, which are configured using points G - J. They are dependant on the charge capacity, or “C” of the pack. We’ll discuss this in more detail when it comes time to configure these jumpers.

DN1 • 7

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Ramsey Electronics DN1 manual
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DN1 specifications

Ramsey Electronics DN1 is a versatile and compact digital audio transmitter that caters to a variety of audio transmission needs. It is designed for hobbyists, educators, and DIY enthusiasts looking to create their own wireless audio systems. The DN1 offers a reliable solution for transmitting audio signals over short distances without the clutter of wires.

One of the main features of the DN1 is its ability to transmit audio in the FM band, which provides clear sound quality and minimizes interference. The device operates at a frequency range of 88 to 108 MHz, allowing users to choose the optimal frequency for their specific environment. This adaptability makes it suitable for applications like personal broadcasting, classrooms, or small events.

The DN1 is equipped with a simple-to-use interface, featuring adjustable audio input levels and an LED indicator for power and modulation status. It supports both mono and stereo audio inputs, making it a flexible option for various audio sources. Users can connect the transmitter to devices such as audio players, microphones, or computers, which allows for seamless integration into existing setups.

Another significant characteristic of the DN1 is its compact and lightweight design, making it easy to transport and mount in different locations. Its robust construction ensures durability, making it ideal for both indoor and outdoor use. This makes the DN1 an excellent choice for users who need a portable solution for DIY projects or presentations.

The device operates on a low-power consumption model, which is not only environmentally friendly but also cost-effective. It can be powered by a standard 9V battery or an external power supply, adding to its convenience and versatility.

In terms of performance, the DN1 boasts a transmission range of several hundred feet in optimal conditions, ensuring that audio signals remain strong and consistent even in larger areas. This range, combined with its ease of use, makes it an appealing option for those looking to broadcast audio without the limitations of wired connections.

Overall, Ramsey Electronics DN1 stands out as an innovative transmitter that brings together user-friendly features, excellent audio quality, and practical design. Whether for personal use, educational purposes, or event hosting, the DN1 meets the demands of modern audio transmission needs, allowing users to experiment and expand their audio capabilities with ease.
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