Interfacing a Picaxe to the 45s voice recorder

I’ve built the 45-Second Voice Recorder featured in the May 2005 issue and it works fine. However, I’m trying to interface it with a PICAXE 08M and have encountered some difficulty. Should the output of a PICAXE be enough, when toggled from low to high then back to low, to activate the rewind/playback of the chip when directly connected to pin 23 (/M7_End) of the HK828 via the 10-pin IDC header? Or do I require extra components?

My original plan had been to replace the Rew/Play switch with a small relay, although I would prefer to interface more directly. (B. B., via email).

It should be possible to control the HK828 voice recorder IC with a PICAXE micro. A falling edge on M1-bar (pin 1) initiates playback, so you’d set the chosen PICAXE port bit as an output, idle high. You’d then pulse it low and back high again. Experiment to find the minimum pulse width – 100ms would be a good starting point.

Refer to the HK828 datasheet for more information. It’s available from www.honsitak-taiwan.com/list.files/list_pdf/hk828-2.pdf

High power 13.5V
DC supply

I’m looking for a project published years ago in SILICON CHIP or "Electronics Australia" magazine. It was a high current 12V supply using phase-controlled SCRs in the primary side of the transformer. Any ideas as to when it might have been? (R. C., via email).

The project you refer to was a 13.5V 25A power supply for amateur transceivers, published in the May & June 1991 issues of SILICON CHIP. It used a Triac in the primary of the transformer. We can supply the back issues for $8.80 each, including postage.

Garage door
remote controller

I am building the Garage Door Remote Controller featured in the October 2004 issue. On testing using the manual button on the PC board, the correct response is obtained; ie, Stop, Up, Stop, Down, Stop, Up, etc. However, when using the remote, I usually achieve Up, Down, Stop. It hardly ever stops until it has done a reverse. Why is this so? The above tests have been done on a small 12V motor not connected to anything.

Then, when I connect it to the motor coupled to my garage door, it failed to lift the door up (it got up about 30cm) and simply stopped. I have adjusted VR1 and VR2 in various ways to no avail. On a closer inspection, I realise that the output current draw for the kit is not enough to power my motor and lift the door up. Is there a way to increase the current output on the receiver unit or do you have a better suggestion? (R. E., via email).

It’s possible that you have a fault in the RF module. Check that it is properly soldered to the PC board and that the supply is 5V. If these checks are OK, you may need a new module.

As far as the limit current is concerned, you can increase this by reducing the sense resistors to 0.1Ω or by increasing the 220kΩ resistors associated with IC3a & IC3b.

Enhancing The Video Enhancer I refer to the Video Enhancer & Y/C separator described in the August 2004 issue of SILICON CHIP. I have constructed this unit and found that although the adaptive digital comb filtering works well, the edge enhancement does not. Because of the low bandwidth (3MHz) of VHS recordings, the rise time of the highest frequency luminance edges exceeds 100ns. The circuit explanation for the video enhancement states "all signal changes which last longer than selected delay lines will be cancelled out". I have found that the output of the enhancer with VHS video is essentially zero. The enhancer is bypassed during sync because, as per the article, spikes would be added to the sync. The sync rise time from a VHS recording is about 300ns which exceeds the length of the delay lines by a large amount and would therefore not suffer distortion with spikes on edges. I have checked the circuitry very carefully and all appears to be as it should be. I would appreciate your comments. (D. M., via email). The length of the longer delay line in the Y/C Separator/Enhancer was indeed something of a compromise, because the full cable length necessary to give a good measure of enhancement to low-bandwidth VHS signals was around six metres. This length was almost impossible to fit inside the box, so we reduced it empirically to a length which still seemed to give useful enhancement using the prototype. If you want to achieve better enhancement of VHS signals, you might care to run a short length of cable from the "DL2" terminal pins on the PC board out to a BNC socket added to the rear panel of the box and then use this socket to connect a suitable long length of cable coiled up neatly outside the box. The external cable would have a BNC plug at one end and a short circuit at the other, of course. This external cable arrangement would let you experiment with round-trip delay times and let you achieve the optimum edge enhancement for your system.

UHF/VHF tuner project for older TV sets

I have an old B&W VHF-only TV set sitting in my spare room which I would like to be able to use if I could "upgrade" it to also handle UHF and perhaps also digital as well as analog. My suggestion would therefore allow for any old B&W or older colour TV set to be brought back into service.

My idea is that the project might include either a separate VHF & UHF selector knob or an "up" and "down" button with an optional remote control available for both versions. Also, if suitable "black box" tuner units were available that would simplify the design, then so much the better.

Among the features of the "adapter" during the construction process would be the ability to either preselect a VHF output channel or allow the user to select the VHF output channel to be fed into the TV when installing the unit. The unit would be powered via a low voltage plugpack and would be located external to the TV as per the attached diagram. Since drawing the diagram I have just noticed that the addition of a 2-digit channel display would be required in the "up and down button" model. (P. M., via email).

The solution to your quest is quite simple: use any old VCR, preferably one with a working remote control. It will tune over the entire UHF and VHF band. Just plug its modulated output into your old TV’s aerial socket.

Reverse display for Speedo Alert

In your Speed Alarm kit (November & December 1999 issues), can you tell me how I can get the display to show in reverse? (R. W., Wellington, NZ.)

The display cannot be shown in reverse without changing the lookup table that determines which segments are driven for a particular number to be displayed. This table is located within the software. We have not published or written any revised code for this although it is a very simple change in the lookup table to rearrange the segments that are driven.

Deep Cycle Battery Charger Has Low Output I have finished building the Deep Cycle Battery Charger (November & December 2004). It all seems to be functioning but I have a question. The battery voltage reported by the unit seems to be lower than what I measure at the battery with a multimeter. For example, the charger shows 14.2V but a measurement across the battery terminals reads 14.5V on a digital multimeter. As you can imagine, I am a bit worried about cooking some expensive batteries. Is this normal or is there some further testing I can do to find out if there is a problem? I did all the testing and test-point measurement and setup as per the article and it all looks good. (B. D.,via email). The circuit was designed to compensate for voltage drops across the leads. Make sure you used the specified length and gauge of wire. Alternatively, you can slightly recalibrate the battery reading so it is correct. So adjust VR4 a little for the display reading.

Motorcycle power for GPS unit

I use a GPS on a motorcycle quite often. My son and I go riding in the bush and the GPS stops me from getting lost. I have a problem with the GPS switching off due to battery bounce from the bike vibration.

I want to run the GPS from the power lead but my bike is a 1984 model with AC electrics (6V). I was looking for a voltage converter that will step up the 6V AC to somewhere around 10-12V DC as my GPS will run from 8-30V (Garmin GPS12cx). Would the 3V-9V DC-DC converter from March 2004 issue be suitable for this application with some mods or have you produced any other kits that would be suitable? (C. L., Ingham, Qld.)

The 9V DC-DC Converter has a maximum output current of 100mA (ideally), which is probably too low for your GPS. One possible solution would be to modify the "Adjustable DC-DC Converter for Cars" (June 2003). Assuming a 6V AC input and 13.8V DC output with about 500mA maximum load, the following changes to the converter will be required:

(1). Replace the two 1000μF input capacitors with 2200μF 25V low-ESR units (Jaycar RE-6330).

(2). Replace the 1nF capacitor connected to pin 3 of IC1 with a 680pF ceramic disc type.

(3). Replace the 0.1Ω 5W resistor with 2 x 0.33Ω resistors (1W or higher) connected in parallel.

(4). Replace MOSFET Q1 with a "logic-level" type; eg MTP3055EL or Jaycar ZT-2271.

(5). Replace D3 with a wire link.

(6). Using the specified wire diameter (1.0mm), increase the number of turns on L1 so as to make one complete layer without gaps. We expect that the toroid will accommodate at least five turns more than specified in the construction details.

(7). Wire up a 2A (or higher) bridge rectifier (eg, Jaycar ZR-1314 or ZR-1360) between the AC input leads and the converter’s 12V DC input terminals.

After construction, be sure to adjust and test the unit on the bench using a transformer and a dummy load. You can use the 6.3V tap of a type 2155 transformer (eg, Jaycar MM-2002) and a 68Ω 5W resistor would make a suitable load (it will get very hot!). Adjust VR1 to get 13.8V at the output.

Once the unit has been tested, the entire assembly should be thoroughly cleaned and all components (apart from the 0.25W resistors) securely glued to the PC board to prevent vibration related problems later. Depending on your installation, you will probably also need to seal the case to prevent moisture ingress. Spraying the assembly with circuit board lacquer may also help.

You might also consider an off-the-shelf solution such as Jaycar’s DC-DC Step-Up Converter (Cat. AA-0264) coupled with a rectifier and filter.

Notes & Errata PICAXE-Powered Thermostat, Feb- ruary 2006: the reset signal from the output of the PICAXE is coupled to the rest of the circuit via a 100nF capacitor, whose output is connected to ground via a resistor. On the circuit (Fig.1), this resistor is shown as 22kΩ in value, whereas on the overlay diagram (Fig.2), it’s shown as 20kΩ and in the parts list as 100kΩ. Although all of these values will work, the correct value is 22kΩ. IO Controller, November 2005: the Windows-based software program can crash after running for an extended period – ie, when the logger reaches its maximum 2048 number. This bug has been fixed and the revised software posted on the SILICON CHIP website.

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.