Many applications require a low-distortion sine wave which tracks the clock from a microprocessor. For most designs, this involves a digital/analog converter (DAC), sine table in read-only memory (ROM), and a timer. The maximum sampling rate of DACs which are included in many microcontrollers limit the maximum frequency of the sine wave to approximately 30 kHz.
However, you can use the switched-capacitor band-pass filter MSHFS5 IC to generate a low-distortion (0.5%) 1 MHz sine wave. The circuit uses two high-performance Si-Gate CMOS counters for the clock dividers. The MSHFS5 is a switched-capacitor, selectable low-pass/band-pass filter with six settings. In this application, 1/6th -octave band-pass filter setting provides the lowest-distortion sine wave, for a constant sine output.
For amplitude-shift keying (ASK) or AM applications, the Butterworth low-pass setting provides better impulse response. The clock is 12.5 times the input frequency to center the band pass. The MSHFS6 samples at twice the clock rate, reducing the sampling error when compared to other filters.
The 74HC390A and 74HC393A are high-performance CMOS ripple counters, capable of dividing clocks up to 50 MHz. The 74HC390A is a dual, divide-by-2/divide-by-5 counter, while the 74HC393A is a dual binary counter. For 1-MHz sine-wave output, the master clock of the system is set to 50 MHz.
The 74HC390A divides the clock by 50 to obtain the 1-MHz square-wave input. The 10-kΩ resistors divide the CMOS level clock to one-half its amplitude. The ac-coupling allows the MSHFS5 to bias the input at mid-supply (2.5VDC). The 74HC393A provides a divide-by-4 clock for the master clock (12.5 MHz). To reduce clock noise, apply the clock to the MSHFS5 through a 1-kΩ resistor. Figure 1 shows the schematic for this circuit.
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Figure 1: Sine-wave source circuit schematic.
Figure 2 is a photograph of the waveform on an oscilloscope.
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Figure 2: Resultant waveform shows low distortion achieved.
Total harmonic distortion (THD) is measured at 0.26% using a Krohn-Hite 6900B distortion analyzer. The sine-wave output tracks the clock input down to a 5-Hz clock (0.l Hz sine wave). Newer PIC microcontrollers, such as the 24HC family, will operate with an external clock as high as 64 MHz, and with timers to provide the clock control needed for a swept-sine application.
About the author
John Ambrose is the applications and systems engineering manager at Mixed Signal Integration Corp., San Jose, CA.
Are you a real estate agent looking for marketing ideas in 2015?
My primary piece of advice is that you need to put your customers' needs first. While all forms of marketing should encourage your audience to eventually do business with you, your approach needs to be subtle and less self-serving. In 2015, your marketing strategy should focus on humanizing your business and automating things when you can.
I recently put together an infographic that outlines how agents spend their marketing dollars and compared it to where they're getting their leads from. As I researched this topic, two things became very apparent:
75 percent of a real estate agent's business comes referrals and word of mouth.
But agents are still spending way too much money on new lead sources, rather than investing in their existing clients.
Simply put, if most of your business is coming from your past clients and it costs you six to seven times more to acquire a new customer than it does to retain an existing one, then you should focus your efforts on marketing to your past clients.
The post I wrote last year titled “7 Marketing Ideas for Real Estate Agents in 2014” quickly became the most viewed post on our site (over 20,000 unique viewers). So for 2015, I came up with 10 marketing ideas that agents can use to really help grow their businesses.
1) Be Mobile and Responsive
In 2014, I stressed that going mobile was important in terms of you posting to your social networks while on the go. This is still true today, but this year, I want to stress the importance of being mobile accessible.
You cannot avoid it anymore. Your website and emails need to be designed for all devices and screen sizes and be responsive. Sixty-six percent of emails are opened on a phone or tablet. Facebook has more than 650 million daily active users on mobile devices. And mobile traffic to websites now accounts for almost 30 percent of visits. In short, there are plenty of reasons why you need to be sure that your business is mobile ready.
How It Helps: Being mobile-friendly ensures whoever reads your emails or visits your website has a good experience and that this experience creates a positive perception of your business.
2) Use GIFs in Email
You've all seen GIFs before; they're those soundless graphics that automatically play on a loop. They're great for getting a quick laugh, but these days, they're more often used to caption a situation and convey human emotion without using words. For example…if it's Monday morning, and I'm having a tough time getting motivated, I might text or email this GIF to my friends:
Marketing ideas – GIF use in email
i agree !!