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Ramsey Electronics CT255 - page 1
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. • Visibly counts up to the current tempera tur e in binary numbers ! ...
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Ramsey Electronics CT255 - page 2
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 nsmi tter RAMSE Y RECEI VER KI TS • FR1 FM Broa dcas t Receiver • AR1 A ir cr aft Band Recei ver • SR1 Shortwa ve Receiver • SC1 Shortwav e Co ...
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Ramsey Electronics CT255 - page 3
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 ................. ......... 13 Parts Layout Diagram ................ ... ... 14 Parts List ................ ... ...
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Ramsey Electronics CT255 - page 4
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. This ...
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Ramsey Electronics CT255 - page 5
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. It is a s pecialized part th at i s pre-calibrated at th ...
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Ramsey Electronics CT255 - page 6
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 4.67V. We then figure what the voltage will be across R38 wh en all ...
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Ramsey Electronics CT255 - page 7
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. ...
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Ramsey Electronics CT255 - page 8
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. W hen the U1:B comparator output is high, the oscillator stops. This is ho w the coun t is “he ...
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Ramsey Electronics CT255 - page 9
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. First off we need to set ...
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Ramsey Electronics CT255 - page 10
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 377.8m V at 100.0 F . So to convert 377.8mV to 1.965 ...
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Ramsey Electronics CT255 - page 11
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. Our value would then be 64 + 32 + 16 + 2 or 114. Our ...
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Ramsey Electronics CT255 - page 12
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 5.96E-8, which is considera ...
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Ramsey Electronics CT255 - page 13
CT255 • 13 CT255 SCHEMA TIC DIAGR A M ...
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Ramsey Electronics CT255 - page 14
CT255 • 14 CT255 PARTS LAYOUT DIAG R AM ...
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Ramsey Electronics CT255 - page 15
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 cit ors [C2,7] 1 470 µF electrolytic capacitor [C8] Resistors 8 390 ohms (orange-w hite- brown) [R5,6,7,8,9,10,11,12] 1 1K ohms (brow n-b ...
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Ramsey Electronics CT255 - page 16
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. • Use only rosin-c ...
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Ramsey Electronics CT255 - page 17
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. Since you may apprec i ate som e w arm -up soldering practice as w e ll as ...
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Ramsey Electronics CT255 - page 18
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. Identify C8, the 470 uF electrolytic capa citor (sm all cylindrical component coated with plas ...
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Ramsey Electronics CT255 - page 19
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. P ay particular att ...
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Ramsey Electronics CT255 - page 20
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). 19. Install R4, 10K ohm (brow n-black-orange). 20. Inst ...
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Ramsey Electronics CT255 - page 21
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. After soldering bend it over to a 90º an ...
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Ramsey Electronics CT255 - page 22
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. Remember that the temperature sensing circuitr y is relying on a ver y small voltage measurement to determine the temperature, so use a good qua lity shielded ...
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Ramsey Electronics CT255 - page 23
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. ASSEMBLY INSTRUCTIONS FOR CUSTOM CA ...
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Ramsey Electronics CT255 - page 24
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. 5 to 12DC po we r supply (n oting that t he center pin of the power supply is the positive co nnec tion) and watch your th erm ometer count up the first of man ...
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Ramsey Electronics CT255 - page 25
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. The input shou ld be whatever the sup ply v olt- age is specified at ...
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Ramsey Electronics CT255 - page 26
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. CONCLUSION We sincerely ho pe that you enjoy the use of this Ramsey product. As always, we have tried to co m pose our manual in the easiest, most user-friendly format that is possible ...
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Ramsey Electronics CT255 - page 27
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. T he very fact that y ...
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Ramsey Electronics CT255 - page 28
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.com REQUIRED TOOLS • Soldering Iron ( W LC100) • Thin Rosin Core Solder (RTS12) • Needle Nose Pliers (MPP4 or RTS05) • Small Di agonal Cutte rs (RTS04) ADDITIONAL SUGGESTED IT EMS • Helpin ...
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