HT1621B Display controller Breakout Board

As a part of my work, I needed to drive an LCD segment display. Now, these displays are somewhat of a mixed breed between LCDs and 7 segment displays. They look sleek like LCDs, and are structured like 7 segment displays. However, they cannot be controlled just by toggling the segment pin of a particular segment high. They actually expect something of an “AC” signal to keep them on.

There are Arduino libraries that allow you to do this : You can find it here . However, if you are going to need 8-9 pins to control one character, you’ll find you will quickly run out of pins. Thankfully, these segments are very common, and so of course, there are controller ICs that will drive these displays, and let you offload the cumbersome task of generating the AC signals to drive those LCDs. The HT1621B is the perfect LCD segment controller IC for this job.

You just have to send messages serially to the HT1621B (in the right format of course), specify the necessary parameters, and the controller will take care of the rest. You can use the Arduino library for the HT1621B here.

HT1621B Breakout board

While working on this, I found it rather difficult to find an existing breakout board for the HT1621B, which is in the SOP48 package. I designed a board for it so that I could test it out. You can order the board with HT1621B controller ( if you are in India ) at the Amazon link here : .

If you want to get just the SOP48 breakout board, you can head over to OSHPark (link below).

Order from OSH Park

I hope this is useful !

Wireless Spectrum in India

I got curious about allocation of wireless spectrum in India, and I did a bit of digging to understand what bands were allocated for what purposes. My interest in this was partly to investigate what frequencies were license-free, so that they could be used for hobbyists, personal and civilian communication networks without applying for licensing.

I found this information in the National Frequency Allocation Plan (NFAP), which I have linked to below. Apparently, the NFAP is reviewed every 2 years, and the last document I found was the NFAP-2011. The Wireless Planning and Coordination Wing (WPC) of the Ministry of Communications and Information Technology puts out this information.

There is a graphic chart from 2002 (linked below), but it is not up-to-date, so use it with caution. For all intents and purposes, the NFAP-2011 is the most up-to-date information available (conditions apply).

The spectrum is allocated by means of gazetted notices and circulars, and as such there is no single Act or Law which deals with allocation of specific frequency bands. After perusing a few circulars which deal with allocating frequency bands for “unlicensed” usage, I find that the following bands are available for use without any licenses from the relevant authorities. Each of these come with maximum emitted power in specified bandwidths.

1. 50-200 KHz –  GSR90(E) dated 10.02.2009
Tyre pressure indicator systems for use by airlines during all phases of flight, vehicle security system and other low power devices are the intended use case.

Base unit: 1610, 1640, 1675, 1690 kHz, 43.720, 43.740, 43.820, 43.840, 43.920,
43.960, 44.120, 44.160, 44.180, 44.200, 44.320, 44.360, 44.400, 44.460, 44.480,
46.610, 46.630, 46.670, 46.675, 46.710, 46.725, 46.730, 46.770, 46.775, 46.825,
46.830, 46.870, 46.930 and 46.970 MHz.
Remote Unit: 26.375, 26.475, 26.575, 26.625, 48.760, 48.840, 48.860, 48.920, 49.020,
49.080, 49.100, 49.160, 49.200, 49.240, 49.280, 49.360, 49.400, 49.460, 49.500,
49.670, 49.770, 49.830, 49.845, 49.850, 49.860, 49.875, 49.890, 49.930, 49.970, 49.90,
150.350, 150.750, 150.850 and 150.950 MHz.

The above frequencies are earmarked for cordless Telephones, if you are developing such a system.

1820-1860 kHz
3500-3700 kHz
3890-3900 kHz
7000-7200 kHz
14000-14350 kHz
18068-18168 kHz
21000-21450 kHz
24890-24990 kHz
28000-29700 kHz
50-54 MHz
144-146 MHz
434-438 MHz

Amateur Service is permitted in the above bands.Amateur Service means “Amateur Radio” or Ham Radio, but you need to get a license from the WPC for using it (you have to pass an examination as well).

4. 3213, 5218, 13862.4 kHz, 73.675, 79.025, 159.55, 436.525 MHz
The above frequencies are earmarked for temporary demonstration of equipments and do not require licenses. These might be usable for experimental purposes, but too much information was not available about these bands.

5. 13.553 -13.567 MHz
The above band is available for unlicensed use for very low power radio devices. This band is used by the NFC standard (Near Field Communication) on contactless cards

6. 26.957-27.283 MHz
The above band is available for unlicensed use subject to a maximum radiated power of 5W.

7. 433-434 MHz
The above band is available for unlicensed use subject to a maximum radiated power of 10 mW with a channel bandwidth within 4Khz

8. 335.7125, 335.7375, 335.7625, 335.7875, 335.8125 and 335.8375 MHz,
The above band is available for unlicensed use for remote controlling cranes with a channel bandwidth of 10 KHz and maximum transmit power of 1 mW

9. 402-405 MHz
The above band is available for unlicensed use for very low power remote cardiac monitoring RF wireless medical devices,medical implant communication/ telemetry systems and other such medical RF wireless devices.

10. 926 – 926.5 MHz
“Certain spots” in this band are “open for consideration” for very low power cordless telephones.

11. 1427 – 1535 MHz
This band  may be “considered” for “experimental/ trial/ pilot-study purposes for indigenously developed technologies for point-to-point backhaul and point-to-multipoint access systems” based on request.

12. 2.4-2.4835 GHz
The above band is available for unlicensed use and is used for WiFi, Bluetooth, Zigbee, and many others.

13. 5.150-5.350 GHz , 5.725 – 5.875 GHz
The above band is available for unlicensed use and WiFi routers have started using this band. It may also be used for very low power radio gadgets, radio toys, Dedicated Short Range Communications (DSRC) for Intelligent Transport Networks etc.

14. 5.57 – 5.725 GHz
The above band can be made available on request.

15. 6.0-7.25 GHz
The above band can be used for Ultra Wide Band Equipment.

16. 865-867 MHz
The above band is available for unlicensed use for low power wireless equipment. Please note that 868MHz is not included in this unlicensed band, which is available in other regions for LoRa equipment.

1. Most allocations of frequency are done on a non-exclusive basis, which means they are to be shared.
2. The power levels of communications on the frequencies must be within specified limits to avoid interference. Your unlicensed communication, as a general principle, is not allowed to mess with somebody else’s licensed, or even unlicensed communication.
3. The spectrum allocations are non-permanent and can be changed.
4. Even though you do not need a license to use some of the bands above, you still need to apply for a license to make, sell or import the hardware that makes of these bands. This seems cumbersome, but I expect it is intended to ensure compliance to the regulations.

Links :

1. National Frequency Allocation Plan 2011
2. National Frequency Allocation Plan 2002 Chart

This note is very much a work in progress. I am compiling a much more detailed document for the technically/ business-oriented, please get in touch if you to know more specific information.

Also, I do not guarantee the completeness or acccuracy of this information, as this note is a compilation from available pieces of scattered information from hard-to-find government notifications.