How the counter oscillator works

U1:D is set up as a simple oscillator to generate our clock pulses that drive the ripple counter. When the comparator U1:B output is low, this circuit will run normally, generating pulses for our counter. When the U1:B comparator output is high, the oscillator stops. This is how the count is “held” for display. This oscillator works through the same principle as the comparator, by comparing the charge voltage across C1 charged through R1 to the voltage at pin 12. When the output of U1:D is our max of 5V and the output of U1:B is 0V (running mode), the voltage at pin 12 should be about 3V (R4, R2 and R3 act as a voltage divider). At this point C1 is charging through R1 over a period of time. Eventually its charge will surpass our 3V at pin 12, where the output of the opamp comparator will switch to low. This makes our voltage at pin 12 about 1.6V. Now the capacitor C1 discharges until it surpasses 1.6V in the opposite direction, and the output switches back to high. This repeats over and over and is the basis of our oscillation. The reason why the oscillator stops when the output of U1:B goes high is the voltage at pin 12 becomes a level that the charge on C1 can never reach. It is greater than 5.0V due to R15 limiting the voltage on C1 to 3.4V, so the comparator function is disabled.

Restarting the conversion cycle

Now our count stops at a certain voltage, but how do we make the count reset every so often so we can get a new reading? Simple. We have another opamp stage that is set to be yet another comparator. In this case we are comparing the voltage between R30 and R34, in this case 2.5V, to the charge on C2. C2 charges through R24 in about 5-6 seconds. This capacitor charges while the output of U1:B is in the disable count mode with the output being high. Once the charge on the capacitor surpasses the 2.5V threshold, the output goes high, clearing the count on the ripple DAC.

This in turn re-enables the oscillator of U1:D since U1:B compare values are reset, and C2 then discharges quickly through D9 to get ready for the next round starting with the first clock pulse in U1:D. C2 does not charge until the count is complete, so the reset cycle will hold the finished count long enough to be seen.

For the complicated Fahrenheit design

Skip this section if you don’t want a bad headache.

Now how do we switch to Fahrenheit? Not a simple as it sounds. For one our Celsius to Fahrenheit conversion is listed as:

F = 9/5 * C + 32

We see by this formula that not only do we have to scale by 9/5 we also have

CT255 • 8

CT255 specifications

The Ramsey Electronics CT255 is a versatile and advanced communication tool designed for radio enthusiasts and professionals alike. As a 2-meter FM transceiver, it is known for its robust performance and extensive feature set, making it ideal for both casual users and serious operators.

One of the standout features of the CT255 is its compact design, allowing for easy integration into various environments such as home stations or portable setups. The unit is built with user-friendliness in mind, featuring an intuitive interface with a clear display and easily accessible controls. This ensures that users can quickly tune into their desired frequencies and modify settings without extensive technical knowledge.

The CT255 operates on a frequency range from 144 to 148 MHz, providing access to the popular 2-meter amateur radio band. This frequency capability is complemented by an impressive output power of up to 25 watts, ensuring robust communication over extended distances. It also includes a built-in automatic repeater shift, which simplifies contacts through repeaters, making it an excellent choice for those looking to enhance their communication range.

In terms of technology, the CT255 employs advanced digital signal processing (DSP), which significantly improves audio clarity and reduces background noise. This makes communication clearer, even in less-than-ideal conditions. Additionally, the transceiver features an array of scanning functions, including memory scan and priority scan, allowing users to monitor multiple channels effortlessly.

The CT255 comes equipped with multiple memory channels, enabling easy access to frequently used frequencies. This feature is particularly useful for users who participate in various nets or have multiple repeaters they commonly contact. Moreover, the unit supports CTCSS and DCS tones, which adds an extra layer of privacy and reduces interference from unwanted transmissions.

Safety and durability are also key characteristics of the CT255. The robust construction ensures it can withstand the rigors of regular use, making it suitable for field operations. It is designed with heat dissipation features to prevent overheating during prolonged use, ensuring reliability during critical communications.

In conclusion, the Ramsey Electronics CT255 is a well-rounded transceiver that brings together advanced technology, user-centric design, and excellent performance. Its range of features makes it an appealing choice for radio amateurs seeking a dependable and efficient communication solution. Whether for casual chatting or emergency communications, the CT255 stands out as a reliable tool that meets the demands of modern radio users.