After skiing or a long walk in the autumn impassability of roads shoes often gets wet through. Upon returning home her hurry to be dried, given that she gonna need it again. And here it is important to ensure that your shoes during drying is not dried up, otherwise it will lose shape and covered with cracks.
In order not to waste time on a systematic check of the condition of the shoes to entrust this to a machine. Controlled parameter can serve as the electrical resistance of the material of the Shoe, which, depending on humidity varies from hundreds of Ohms (in raw state) to tens of ohms or higher (dry). Control functions successfully performs a device, scheme of which is shown in figure.
On DD1 chip, consisting of several logical elements 2I-NOT collected two generators of electric oscillations, differing from each other only by frequency switching. On the elements DD1.1, DD1.2 assembled generator with switching frequency approximately 1 Hz. Its output signal is amplified by a power amplifier on transistor VT1, and then is used to control the led HL1. Generator on the elements DD1.3, DD1.4 generates oscillations of audio frequency, after which the gain of the amplifier transistor VT2 arrive at the dynamic head of BA1.
With controlled resistance Rx is connected the first generator. It performs the functions of leading and determines the mode of the second generator. Input 2 of the element DD1.1 through the resistor R2 is connected to the midpoint of the voltage divider formed by the resistor R1 and the resistance Rx. While your shoes are wet and the resistance Rx is small, input 2 DD1.1 has the low voltage level, causing the operation of the generator blocked. The voltage at the output 4 of the element DD1.2 also has a low level. Similarly, work is blocked and the second generator. In this case transistors VT1, VT2 are closed and do not consume current from the battery GB1.
When footwear is dry and its resistance Rx increases, the first generator will start to work, as reported by the blinking of the led HL1. In moments, when the output 4 element DD1.2 will present a high voltage level, earn the second generator. At the output there is the sound signal. Under its influence will sound emitter BA1. The current consumed by the emitter head, limits resistor R8. Resistor R1 sets the resistance Rx, which device should work.
As probes X1 you can use two flexible strips of stainless metal, paper gasket pressed against the inner walls of the toe of the Shoe, helping thereby to maintain the shape of the Shoe. If necessary, the selection of the capacitance of the capacitor C2 achieve the maximum volume of the sound emitter.
The device is recommended to use fixed resistors MLT-0,125, AC SP-0,4, capacitors KLS (C2) and C50-6 (C1). Power switch - series MT or PDM. The sound projector is dynamic head 0.25 HDS-7 the resistance of the voice coil 50 Ohms. Fit and a Cup with the same or are some great resistance. Power supply - battery "Krona" or two the series-connected battery 3R12. Avoid quick discharge galvanic source during drying his shoes should be kept away from heater.
Author: Yu Prokopcov, Moscow