Instruction/ maintenance manual of the product CT255 Ramsey Electronics
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CT255 • 1 COMPUTEMP 255 BINAR Y THERMOMETER KIT Ramsey Electronics Model No. CT255 A really neat educational kit to learn the p rinciples of binary math, how simple digital to anal og converters work, and how instrumentation amplifiers ma y be used to measure the environment.
CT255 • 2 RA MSEY TRA NSMIT TER KITS • FM100B Professional FM Stereo Tr ansmitter • FM25B S yn t hesized Stereo FM Transmitter • MR6 Model Rocket Track ing Transmi tter • TV6 Television Tra .
CT255 • 3 COMPUTEMP 255 BINAR Y THERMOMETER KIT Ramsey Pu blication No. MCT255 Price $5.00 TABLE OF CONTENTS Introduction ..... ................. ................ 4 Circuit Description ........ ................. ... 5 Schem atic Diagram ............
CT255 • 4 INTR ODU C TION Years ago Ramsey Ele ctronics had a really neat little kit called the CompuTemp 127. This was a favorite k it purchased by man y who w ere into the electronics hobby in the ‘70s and ‘80s. It was unfortunately retired to make space for a growing list of other popular kits being adde d to the catalog at the time.
CT255 • 5 CIRCUIT DESCRIPTION There’s a lot of c ircuitry in the CT 255 that is in us e to this day in a variety of circuits. We will begin with the temperat ure sensor itself, detailing how we di d this 20 years ag o a nd how we do it now. The actua l temp erature sens or is the LM 35DZ.
CT255 • 6 The DAC (Digital to Analog Converter) The resistor values in th is ladder are ch osen to give us nice even steps in the voltage range w e are able to work with. The outputs of the counter can’t actually achieve 5 volts with the LEDs on the output, but really close at 4.
CT255 • 7 in series with the input to reduce any noise that may be pre sent on th e temp erature se nsor to increase a ccuracy of your reading. C3 in the f eedback branch is als o used to re duce noise in the reading . In the Celsiu s jumper setting, R37 an d R2 7 ar e used to adjust th e ga in of ou r temperatu re sen sor f or a Celsius reading.
CT255 • 8 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 com parator U1:B output is low, this circuit will run normally, gene ra ting puls es for our counter.
CT255 • 9 to add 32. W e do this b y switching in R22 into the cir cui t, which combined with R23 adds in the 32 offset that we ne ed. The proble m howeve r is this acts lik e a voltage divider on t he outpu t of U1:A our scaling amplifie r, so now we have to adjust the non-in vertin g amplifier’s gain to compen sa te.
CT255 • 10 At 100.0 degrees Fahrenheit the temper ature sensor will ha ve an output of a value related to Celsius, so to m ake life easier, we will convert to Celsius first. So: C = 5/9(F-32) or C = 5/9( 100—32) which is 37.78 degrees Celsius. This me ans the outp ut of the se nsor should b e 377.
CT255 • 11 128 times to get the most significant LED to change state just on ce . Norm ally an 8 bit number has these si gnificant v alues: Say bits 7, 3, and 0 are on , all others are off . The value would then be 12 8 + 8 + 1 or 137. Say instead bits 6, 5, 4 and 1 are on, all others are off.
CT255 • 12 You may notice though that the smallest st ep in th i s case is 1/256. This 8 bit DSP is unable to accurately represent this number sm aller than 3.906E-3. Most fixed points DSPs howeve r are 16 bit, 24 and 32 bits. 24 bits of resolution means the smallest number w e can re present becomes 1/(2^2 4) which is 5.
CT255 • 13 CT255 SCHEMA TIC DIAGR A M.
CT255 • 14 CT255 PARTS LAYOUT DIAG R AM.
CT255 • 15 PARTS SUPPLIED WITH YOUR C T255 KIT Capacitors 4 .1 µF disc capacitor (marked .1 or 104 or 100 nF) [C3,4,5,6] 1 1 µF electrolytic capacitors [C1] 2 10 µF electrolytic capa .
CT255 • 16 RAMSEY "LEARN-AS-YOU-BUI LD KIT ASSEMBLY There are num erous solde r connections on the CT255 printed circuit board. Therefore, PLEASE t ake us seriously wh en we say that good soldering is essential to the proper operation of your binary thermometer! • Use a 25-watt soldering pencil with a clean, sharp tip.
CT255 • 17 CT255 THERMOMETER ASSEMBLY INS TRUCTIONS Although w e know t hat you are anxious to complete the assembly of you r binary thermometer kit, it is best to follow the numbered assembly steps when building. Try to avoid the urge to jump ahead installing components.
CT255 • 18 installed). Since a diode will only con duct when it i s forward biased, this diode acts as a “reverse voltage” protectio n circuit. Diodes are of ten used as “one- way switches” in this mann er to prot ect internal circu itry. 3.
CT255 • 19 Next we will install some of the outpu t voltage divider resistor netwo rk s. The circuit board has been lai d out to avoid confusion wi th th ese m ultiple row s, and we will try to avoid sounding too redundant when installing them , Remember to save those leads as we will be installing some jumper wires very soon.
CT255 • 20 16. Install C2, 10 uF electrolytic capa citor. Remember to obse rve po larit y with electrolytic capacitors! Check the parts placement diagram for correct orientation. 17. Install R34, 10K ohm (brown-black-orange). 18. Install R30, 10K ohm (brown-black-orange).
CT255 • 21 install all eight so that th ey are in line. A trick may be to f ashion a cardboard “standoff “ and pre-bend the LEDs before installing 35. Install D1, one of the LEDs. The flat side is oriented as show n in the diagram. Leave it standing about 3/4 inch off of the board w hen soldering.
CT255 • 22 40. FOR REMOTE SENSOR OPERATION. If you wish to run the sensor to a remote location, you will need to obtain a 3.5 mm stereo plug and wire as shown in th e f ollowing figure.
CT255 • 23 CONGRATULA TIONS ! Your binary thermometer is now complete! Have a final look over y o ur work, paying particular attention to the orient ation of diodes, capacitors, and IC’s. Remember that any probl ems you find now can s ave time and effort after the unit has been case d up a nd final assembled.
CT255 • 24 USE OF YOUR COMPUTEMP 255 Now we are read y for th e mome nt of truth, the initial po wer up and runn ing of your binar y ther mom eter. Energize the un it with a s uit ab le 7.
CT255 • 25 TROUBLESHOOTING GUIDE If your CT255 does not work at all, recheck the follo wing: • correct orientation of VR1, U1, and U2 (see PC boar d la yout diagram) • You should be able to m easure th e voltage on t he inpu t and output termi- nals of voltage regulator VR1.
CT255 • 26 If all els e fails, call or email Ram sey Tech Support at 585-924-4560 or tech@ramseyelectronics.com. We’ll try to help talk you thro ugh the problem.
CT255 • 27 The Ramsey Kit Warra nty Please read carefully BEFORE calling or writing in about your kit. Most problems can be solved wit hout contacting the factor y. Notice that this is not a "f ine print" warranty. We want you to understand your rights and ours to o! All Ramsey kits will work if assembled properly.
CT255 • 28 RAMSEY ELECTRONICS, INC. 590 Fishers Station Drive Victor, New York 14564 Phone (585) 924-4560 Fax (585) 924-45 55 www.ramseyelectr onic s.
An important point after buying a device Ramsey Electronics CT255 (or even before the purchase) is to read its user manual. We should do this for several simple reasons:
If you have not bought Ramsey Electronics CT255 yet, this is a good time to familiarize yourself with the basic data on the product. First of all view first pages of the manual, you can find above. You should find there the most important technical data Ramsey Electronics CT255 - thus you can check whether the hardware meets your expectations. When delving into next pages of the user manual, Ramsey Electronics CT255 you will learn all the available features of the product, as well as information on its operation. The information that you get Ramsey Electronics CT255 will certainly help you make a decision on the purchase.
If you already are a holder of Ramsey Electronics CT255, but have not read the manual yet, you should do it for the reasons described above. You will learn then if you properly used the available features, and whether you have not made any mistakes, which can shorten the lifetime Ramsey Electronics CT255.
However, one of the most important roles played by the user manual is to help in solving problems with Ramsey Electronics CT255. Almost always you will find there Troubleshooting, which are the most frequently occurring failures and malfunctions of the device Ramsey Electronics CT255 along with tips on how to solve them. Even if you fail to solve the problem, the manual will show you a further procedure – contact to the customer service center or the nearest service center
