PIC rain gauge doesn’t like odd days

I have just completed building the PIC-Powered Rain Gauge as featured in the June 2000 issue of SILICON CHIP. I have been planning such a project since seeing a similar concept in a long-forgotten magazine many years ago which used a mercury tilt switch as a sensor and a telephone exchange subscriber’s meter as a recording device. Your design is a tad more "state of the art" and immediately caught my eye.

I thought that you may be interested in some observations and also be able to comment on one operational aspect of the design.

On initial testing I found that even though the vane passed through the photo detector beam, it did not result in an increase in the count display. I fixed a piece of thin shim brass to the vane which resulted in a 100% accurate count. Could it be that the plastic is transparent to infrared light? It seems unlikely but the brass fixed the problem.

After testing the unit with "real" rain I have concluded that the protective insect screen on the funnel is not such a good idea. I have mounted a conventional rain gauge next to the automatic version as a check on the calibration. The first rain event resulted in a reading in the automatic gauge half that of the conventional gauge.

There may be three reasons for this error: (a) the surface tension of water tends to make drops sit on top of the insect screen and not enter the funnel; (b) drops striking the screen with sufficient velocity tend to break up and not all will enter the funnel and (c) the surface area of the funnel is reduced by the surface area of the screen.

None of the above may be true but after removing the screen, the next rainfall event resulted in 17mm in the conventional gauge and 16mm on the display of the automatic gauge; close enough for me, so I will leave the screen off and regularly check for invasion by creepy crawlies.

This next observation concerns the recording of the previous day’s rainfall. My understanding is that rainfall recorded today will, after the empty time which, in my case, is midnight, be transferred to the previous day’s log and be recorded in "day -1".

Any other previous readings will at the same time be pushed back one day and "day -60" will fall off the edge. In my case, today’s reading is recorded in "day -2" and the next day will be moved to "day -4" and so on, with all recordings in even days and no recordings in odd days. The movement of previous day’s rain seems OK but always stepping two days instead of one day means, in effect, that I can only record 30 days and not 60 days as designed. Could I have done something wrong or have I discovered a bug? (B. C. Ballina, NSW).

The plastic vane entering the light sensor will be detected correctly if the vane penetrates deep enough into the slot. Adding a brass shim probably added the necessary extra depth for correct counting.

The flyscreen mesh should not affect readings. Surface tension of the water droplets will cause some storage in the screen but these droplets will fall through with further rainfall. The screen does not decrease the area of catchment since all water caught within the inside diameter of the 90mm endcap will eventually fall through into the funnel.

The only cause of water loss would be if the rain water droplets bounced off the flyscreen to outside the catchment area. If this is the case, you can form the flyscreen so it is a cone shape inside the funnel. Also raising the lip height around the end cap will help.

The movement of the day’s reading into the second day previous rather than the first day previous suggests that there is a faulty storage register inside your PIC. The least significant digit is not changing but remaining at 0. We suggest that you obtain a replacement PIC (IC1) from your kit supplier.

Also see the Notes & Errata for June 2000.

Electric wok control wanted I hope your staff at SILICON CHIP might be able to create a control for most, if not all, electric fry pans and woks. My electric wok is controlled by a mechanical thermostatic switch. Even though it still works fine (actually, it’s brand new), I find the control range is too sluggish. If I set it to halfway, it cools down to a quarter of the original setting before turning back on. I hope you may be able to design a device similar to, say, a light dimmer switch, which can control the range more accurately. It would need a capacity of 2400W. (W. S., Narangba, Qld). We would not be keen on a phase-controlled Triac circuit (ie, a light dimmer) at such high power. However, we have published a zero voltage switching circuit which is ideal for the job. Have a look at the Heat Controller published in the July 1998 issue. We can supply the issue for $7.70 including postage.

How to test the Theremin

I have built the Theremin project as described in the August 2000 issue but I cannot get any output. I checked the voltage on pin 6 of IC3 and pin 8 of IC2 and they were both 5.7V as expected.

No matter how I adjusted VR1, the maximum voltage I could get was 3V on pin 1 of IC2. No amount of twiddling the IF coils would result in a measurable voltage at the cathode of D1.

I used a signal generator to check the audio stages and injecting a signal at pin 5 of IC2 resulted in a signal through the speaker, indicating the circuit beyond this point is OK.

It appears that none of the oscillator circuits are working. Could this be due to Jaycar substituting a 2N5485 for the originally specified 2N5484 JFETs?

I do not have access to an oscilloscope. What other troubleshooting methods are there for this kit? Do you have AC/DC voltage measurements or some other means of confirming the oscillators are working properly? (B. D., via email).

The Theremin will work with the 2N5485 FETs as supplied with the Jaycar kit. The adjustment of VR2 can be a little touchy though, so you might want to try a multi-turn trimpot.

Testing the rest of the circuit without an oscilloscope could be difficult. You could disconnect the 1kΩ supply resistors (100Ω for the volume oscillator) leaving only one oscillator operating at a time. Bring an AM broadcast band radio close to the Theremin and check that you obtain a whistle in the sound. This would indicate that the oscillator that is connected is working.

Using a torch as an IR illuminator

I recall that you published an article a few years back on converting a normal torch into one that provides an infrared (IR) light source. Can you help me with details of this project? (J. C., via email).

We published an IR illuminator in the March 1995 issue and it could have been put in a torch but we did not do it. On a similar line though, we published a LED stroboscope in the December 1993 and the LED illuminator was built into a torch. However, if you specifically want an IR illuminator, the March 1995 circuit is more relevant.

We can supply both copies at $7.70 each, including postage.

Fence controller changes zap rate I built the Electric Fence Controller in the April 1999 issue. It has worked fine till now. The first sign of any fault was when I noticed that the controller fired about five times instead of once every 1.5 seconds. This fault appears to have resolved itself but I now get only 150V on the high voltage check instead of 340V with the pulse timer disabled. I have checked every component on the board and all appear to be OK. I had spare ICs so I replaced them to prove the originals, again all OK. The only part to check now is T1 for shorted turns which will mean a rewind. I find this doubtful (but not impossible) as the winding of small transformers used to be my job. The material used was nothing but the best and it was layer wound on an automatic winder. I have checked the ratio and pressure tests indicate it is also OK. What should I look for? (D. T., via email). The change in firing frequency from once every 1.5 seconds to five times a second would suggest a problem with the IC2b oscillator. Check that the 10μF capacitor at pin 6 and the resistors at pin 7 are correct and are soldered without dry joints. If you are only obtaining 150V instead of 340V, the fault could be a leaky 7μF 250V capacitor or a problem with the feedback network which maintains the 340V. Check the two 1.5MΩ resistors, the 10kΩ resistor to ground at pin 2 of IC2a and the components between pins 1 & 2 of IC2a. Also Mosfet Q1 may have gone faulty so it cannot charge T1 correctly.

IR version of LED torch

The LED torch featured in the December 2000 issue was interesting. Could the circuit be adapted to use an infrared LED, making an IR torch? The reason I ask this is that the IRLED "spotlight" for CCD cameras doesn’t reach too far. If an IR spotlight of sorts were available, it would make it possible to see things which would otherwise be out of range of the CCD camera in low light or total darkness. Your comments would be appreciated. (S. N., via email).

Infrared LEDs have a lower forward voltage than white LEDs. In practice, if you want an IR illuminator, just connect a string of four or five IR LEDs in series with a 100Ω resistor to a 12V supply. If you want more IR light, just use more series strings in parallel.

Using the Zener tester on transistors

I have built the Zener Diode Tester for DMMs (March 1996) and it works fine. I am curious if it could be modified to use as a breakdown tester for transistors? (N. P., via email).

The Zener Diode Tester can be used to test the breakdown voltage for any silicon device, including transistors, for voltages up to 112V.

RF choke for the LED torch

(1). If you want to build the LED Torch in the December 2000 issue, I have found a 220μH RF choke at Jaycar which is smaller than winding one on a trigger transformer. It is Cat LF 1538 on page 214 of the current Jaycar catalog. (D. H., via email).

(2). I was fascinated by the LED Torch project using a white LED and the ingenious way in which you fitted the works into the space occupied by a single AA cell. Since a kit was not available I decided to build up a circuit on the breadboard and the only problem was the creation of the 220μH inductor.

I didn’t have any spare pulse transformers and they appear to have been deleted from the electronics suppliers catalogs. I built a few inductors on some ferrite cores which I had and these worked after a while (remember, if you use a green LED for the test load, you will only generate 2.6V across it).

Then came serendipity. I used a pre-wound ring cored ferrite suppression choke and got brilliant results. So I then cast around for some ferrite cores to try and wind a smaller coil which would fit into the AA cell version. The first version used a suppression bead which I found in my junk box. 20 turns of fine wire (about 0.2mm) and I had a choke which worked. The core was about 6mm OD, 6mm long with a centre hole about 3mm.

I then purchased a pack of Jaycar LF-1250 ferrite suppression beads. These are 5mm long, 4mm in diameter and with a 1.5mm bore although some of the bores appear larger – nearly 2mm. I selected two with the larger bores, superglued them end to end and wound on about 20 turns. This also worked and I am now ready to tackle the miniature versions when I get some copies of the PC boards.

This could help other readers complete this project. (B. L., via email).

Thanks to these readers for these tips. Dick Smith Electronics are about to release their kit for the torch as well. It will be supplied with a penlite torch for just $14.60 (Cat K-3018).

Using a different spring reverb module I have a large 3-spring reverb unit made by Belton Engineering, which I’d love to build into a home-brew valve guitar amp, using the circuitry from your Spring Reverb Module published in your January 2000 edition. The Belton unit has the following specifications (obtained from Belton’s website) and they differ considerably from the unit used in your design: input impedance 190Ω; output impedance 2.575MΩ. Could you please advise what modifications I would need to make to the circuit for this to work? (P. S., via email). As far as the input side is concerned, you could use our circuit as is because Q1 & Q2 will quite happily drive a higher impedance. On the output side you need a higher input impedance for IC2a and this can simply be done by changing the 100kΩ resistor at pin 5 to say 1MΩ or higher. However, you haven’t quoted signal delay times or signal levels so the result may be a little hit or miss.

VU meter needs auto level control

I have constructed a LED VU level meter for my car stereo, which is purely for aesthetic purposes; ie, regardless of volume, the display should work over most of its displayable range. The only problem is that the stereo does not have a constant volume output and therefore the input sensitivity of the VU meter must be varied each time the volume of the stereo is varied.

Is there a way to obtain a constant volume level from the stereo, so that I won’t have to turn two dials each time I change the volume? (J. P., via email).

Short of building our CD Compressor described in the July 2000 issue, the only way to avoid the need to change the LED VU setting is to take the signal from across the volume control; ie, you have to access the signal from inside the car stereo.

Thorn Atlas B+W TV needs a good home

I have an old valve TV set that I would like to go to an interested collector. It is an old large (59cm?) Thorn Atlas B+W valve TV set, part of a relative’s deceased estate. The cabinet, made of solid wood, is in excellent condition and I think that the internals are all there, although the circuit diagram is only half complete (pasted in the back of the set). It even has the original knobs intact and would make a fantastic restoration project (although most of the work would be internal as the externals are in such good nick).

If anyone is interested, they can contact me at: p_sun@optusnet.com.au

WARNING! SILICON CHIP magazine regularly describes projects which employ a mains power supply or produce high voltage. All such projects should be considered dangerous or even lethal if not used safely. Readers are warned that high voltage wiring should be carried out according to the instructions in the articles. When working on these projects use extreme care to ensure that you do not accidentally come into contact with mains AC voltages or high voltage DC. If you are not confident about working with projects employing mains voltages or other high voltages, you are advised not to attempt work on them. Silicon Chip Publications Pty Ltd disclaims any liability for damages should anyone be killed or injured while working on a project or circuit described in any issue of SILICON CHIP magazine. Devices or circuits described in SILICON CHIP may be covered by patents. SILICON CHIP disclaims any liability for the infringement of such patents by the manufacturing or selling of any such equipment. SILICON CHIP also disclaims any liability for projects which are used in such a way as to infringe relevant government regulations and by-laws. Advertisers are warned that they are responsible for the content of all advertisements and that they must conform to the Trade Practices Act 1974 or as subsequently amended and to any governmental regulations which are applicable.