Magicland Electronics - Kits

SmartStat-Plus Thermostat

The March 2010 issue of Nuts and Volts magazine has an article, by Tom Fox, titled "Make the SmartStat-Plus." This sophisticated thermostat, which was jointly designed and tested by Tom Fox and Matthew Fox, uses two Picaxe microncontrollers. While it performs all the functions of standard digital thermostats it has several unique built-in safety features. These features include: a LOW AIRFLOW ALERT, which signals a possible blower motor failure, loose or broken belt or a clogged air filter, a total system (A/C or Heat) failure which alerts the user if there exists a 6 degree F or greater difference between the actual ambient temperature and SmartStat-Plus's set temperature, a HIGH TEMPERATURE ALERT which occurs when SmartStat-Plus detects a temperature exceediing 95F and a FREEZE alert that indicates a room temperature below 33F.

In addition to all these unique safety features, SmartStat-Plus uses a 5 CPH (cycles per gour) maximum system rate for both heating and cooling, a 5 minute compressor off time and a 20 second heater off time. These features extend the life of the cooling and heating ssytems. To set the CPH on and off times to other rates, you will need to modify the source code which is provided free of charge. If you are at all acquainted with the BASIC computer language this should be an enjoyable and satisfying task.

Source Codes

• SmartStat-Plus - 08M ver 1.1
• SmartStat-Plus--28X1 ver 1.52

Do You Need a Case or a Front Panel?

No. The main reason I used one was to get some nice photos. I recently designed and constructed a Maximum and Minimum thermometer using a Picaxe (actually I used a slightly modified SmartStat-Plus board) design and it is mounted to a wall. (I was unsatisfied by the inaccuracies of even moderately priced commercial Min/Max thermometers) My wife and kids like its looks. It has a beauty all its own. To be honest, making the front panel and drilling the holes in the right spot in the case took longer than putting all three of SmartStat-Plus boards together (Main Picaxe board, airflow board and power supply board). One nice feature of not using a case is that the reslting good air circulation simplifies the placement of the temp sensor. Note: If you do use a case you must make sure you don't have the sensor inside the case or you will get erroneus temperature readings. (It will be a degree or two too high.)

Hints on Air Sensor Placement

When I first worked on the design of SmartStat-Plus I assumed I was going to place the air-flow board next to the filter. However, I got thinking and testing and found all I needed do was place the air-flow board in the hot air register--assuming you always leave that register open. I tested it out there and it works - perhaps even better than if I put it next to the air filter--I saved not only wire but time and effort.

Note: These boards we sell are double sided-boards with plated through holes, and with solder masking and silk-screening! The boards shown in the photos in Nuts and Volts are prototype boards without solder masking and silk screening!

Smart Room A/C Controller

The October 2008 issue of Nuts and Volts Magazine has an article, by Tom Fox, titled "Build a Smart Controller For Your Room Air Conditioner". This controller, which was jointly designed and tested by Tom Fox and Matthew Fox, uses two Picaxe microncontrollers. While the original purpose of the controller was to make possible a walk-in cooler using an inexpensive room air conditioner, also see Magicland Farms, considerable effort was placed in designing it to make it useful in a wide variety of applications. For instance, it can be used as a sophisticated thermostat which adjusts the building's temperature taking into account the present building's temperature AND the outside temperature! This feature not only will optimize the comfort but can save energy.. Another possibility for this project is as a digital readout anemometer that uses no moving parts! The only required modifications to the Smart A/C controller to make these two widely different projects is the PICAXE's program. Many other diverse applications are possible.

In order to write a PICAXE program you will require a PICAXE Programming Editor from Revolution Education, Inc. The latest version of this software is available as a download, free of charge, from the PICAXE website at www.PICAXE.co.uk. This editor is quite sophisticated and easy to use. However, it has a few problems. One problem is that it seems to keep open several files at once. You must be real careful when asked if you want to save the current file. You might just save an old file over a new one and lose all your session's work!

Source Codes

• Smart Room Air Conditioner Controller - 28X1 ver. 1.2
• Smart Room Air Conditioner Controller - 08M ver 1.1

10/04/2008 Update

First off, the boards I ordered from ExpressPCB came sooner than they said so I now have a good supply on hand.

The original room air conditioner I used was an old unit with non-electronic controls. I used a power relay to directly control the A/C's compressor. (I could have used a light bulb put next to the controls, but I didn't) I decided to purchase a new unit (a Haier 8000BTU job from Walmart) that has digital controls. Since it was brand new I hesitated in rewiring it so I located the electronic temperature sensor, and taped two 2700 ohm 1/4W resistors to it. I then connected the resistors in parallel. These parallel resistors were then connected in series with J3 (the Smart controller's compressor relay) and a 24VAC source. When the Smart controller calls for cooling, the resistors heat up the sensor and fools the A/C into thinking the room temperature is above the temperature setting, which is limited, by the manufacturer, to a minimum temperature of 61F. Because of the built-in time delay as well as the A/C own built-in compressor safety features, I recommend setting the controller's delay to 3 minutes--5 minutes is the default setting. So far, the cooler has been working like a charm. I have operated it as low as 38F without problems. Of course, the cooler will only get this cool if the A/C can keep the room cool enough when the compressor is operated nearly continously. This means the A/C must be large enough for the room insulation/size and the outside temperature can't be extreme. When it gets over 90F out I have a problem keeping the 60 square foot (470 cubic feet) room cooler than 55F average temperature. With the temp in the low 70s it can be kept as cool as a regular fridge. Additional insulation will no doubt help here and we are presently modifying the size and insulation of the cooler. No external fan is used since the built-in fan seems powerful enough. I placed the air flow sensor on the air intake. It seems a setting of around 18-20 is optimum for the air flow shutoff--typically I get a reading of 14 (7 deg F difference) when there is no icing taking place.

One other note. The temperature on the prototype of the Smart A/C controller appears to be within 1 F (maybe perfect) of the actual temperature, even though the prototype's power supply puts out 5.05 volts, and not 5.12V. If you use the adjustrable power supply you might want to tweak things a bit if the displayed temperature differs more than 1F from the actual temperature. Caution here: make sure the Smart job's sensor is located out of the case. It gets a couple of degrees warmer in the case than it does in the room.

Note: These boards we sell are double sided-boards with plated through holes, and with solder masking and silk-screening! The boards shown in the photos in Nuts and Volts are prototype boards without solder masking and silk screening!

Jumper Cable Wizard

Jumper Cables are used to "Jump Start" an automobile or other device that uses an electric starting motor. Although jump starting is simple, it can be dangerous - especially if you make a "simple" mistake. All you need do to safely "Jump Start" a vehicle is to use jumper cables to connect the positive (+) terminal of the bad battery to the positive terminal of the good battery and likewise for the negative (-) terminals. However, if it is night, or the markings on the battery are hard to read one usually needs to make an intelligent guess on which terminals are positive and which are negative. If you goof, you may destroy the computer systems on one or both vehicles. Although unlikely, an explosion may even result.

The Jumper Cable Wizard was designed to make Jump Starting a dead or weak 12 volt battery safer and easier. It also has a built-in feature which tells you, with colored LEDs, the condition of a 12 volt battery. It is designed to be connected and attached directly to a set of jumper cables. If you use the Jumper Cable Wizard according to the instructions you will never make a goof in jump starting a battery EVEN IN TOTAL DARKNESS!

Programming and Customizing the HC11 Microcontroller

The book Programming and Customizing the HC11 Microcontroller was published by McGraw-Hill in 2000 and written by Tom Fox. As its title indicates, the primary subject is the HC11 series of microcontrollers. The book starts off simply and then rapidly introduces Motorola Semiconductor's (Now Freescale Semiconductor Inc.) MC68HC11A1P microcontroller, which is perfect for those who want to start to learn about microcontrollers through a hands-on way. In the book, the author then goes on to give detailed description on how to build Mag-11, a HC11 based single-board computer that was designed primarily as a learning tool although it can be used in a multitude of practical applications. The next project in the book is MagPro-11 whose primary purpose is as an EEPROM programmer for the MC68HCA1FN microcontroller. However, since MagPro-11 uses the BUFFALO monitor it also is perfect for those who want to learn how to write software/firmware for the HC11 series. The third project in the book is MagTroll-11 which is a low-cost controller board which uses the MC68HC11A1FC's internal EEPROM as the storage place for the MCUs instructions. The last project in the book is a unique and revoltionary solid-state wind direction indicator which makes use of the microcontrollers internal intelligence to figure out which way the wind is blowing. As far as the author knows, this was the first accurate wind direction indicator that had no moving parts.

While Programming and Customizing the HC11 Microcontroller was published just 7 short years ago, there have been a number of changes. First, Motorola spun off its semiconductor division in 2004 and Freescale Semiconductor Inc. was created. In late 2006 Freescale was purchased by the Blackstone Group but it still retains its Freescale name. Perhaps more importantly here, Freescale has replaced its 68HC11A series of MCUs with the 68HC11E series. As you may know, Programming and Customizing the HC11 Microcontroller was based on the original HC11 series, which was the 68HC11A series. Happily, however, the 68HC11E series chips will work in the projects with only very minor changes in circuitry and software. Also, Freescale has put out an Engineering Bulletin (EB193) to show how to convert from the A series to the E series. This bulletin is available in PDF format. You also might want to download the Technical Book for the E series.

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