84
votes
Accepted
Why do fire and security systems run at 27.6 V?
27.6V is 2 x 13.8 V.
13.8 V is a common voltage for a 12-V Sealed lead-acid battery (SLA) while under float charge. In float charging the AC power supply maintains a constant voltage across the ...
- 33.8k
39
votes
Accepted
Is it possible to jam wireless home alarm systems?
A "denial-of-service" wireless attack is very easy. It will disrupt radio communication between sensor and panel. Hopefully, the panel is smart enough to detect that one (or more) of its sensors has ...
- 27k
37
votes
Why are SRAM based FPGA used more than NVM based FPGA?
The main driver is the fact that SRAM is highly compatible with the same physical process that is used to implement the actual logic. Indeed, most FPGAs these days are based on LUTs (lookup tables), ...
- 177k
30
votes
Why do fire and security systems run at 27.6 V?
This is simply the nominal voltage of lead acid batteries while charging. Think 2 x "12 volt" in series, where the nominal 12 volt is really 13.8 volt.
See for example What should the ...
- 14.5k
24
votes
Why are SRAM based FPGA used more than NVM based FPGA?
In addition to Dave Tweed's answer regarding the fabrication processes involved, most flash-based FPGAs actually still use SRAM to drive their fabric. The bitstream is loaded into the SRAM from flash ...
- 3,454
21
votes
Is it possible to jam wireless home alarm systems?
First of all, to clear some things up: All digital signals are built up by analog signals. As already mentioned in the comments, all wireless communications can be jammed, encrypted or no. And last ...
- 3,807
16
votes
Accepted
How safe is this and should I change it?
So, a small child is playing underneath your table and manages to disconnect one of the earth wires to your newly fitted appliance outlets. Can anybody be aware that this has happened?
Not very likely ...
- 467k
11
votes
securely storing and using keys in an embedded system
I'm sorry this answer won't actually solve your problem. But it is too long to fit in a comment, and it will allow you to rethink your problem in the right way (because as it is, I think it is flawed)....
- 16.1k
11
votes
What is the ideal method of sensing whether 4 points on the bottom of a device are all depressed to indicate contact?
Limit switches might be better options than momentary make push buttons, as they can have longer travel and usually require less force to depress. They are extensively used in things like industrial ...
- 1,440
11
votes
How can I make an alarm circuit which senses both cutting and shorting the wire?
Building on @jsotola's comment. A window comparator coupled with a resistance in the sense line would allow the circuit to detect the open and shorted condition.
Understanding a window comparator
...
- 8,191
8
votes
Why are SRAM based FPGA used more than NVM based FPGA?
More than anything, it depends on your requirements. While Size, Weight and Power (SWaP) are the main drivers for ICs in-general, if you aren't compelled to develop an ASIC because of those ...
- 935
8
votes
A few questions on PIRs and other motion detectors
PIR sensors have quite a few advantages:
they’re very cheap
they use very little power (since they’re passive) – very important for battery powered/wireless sensors. We’re talking microwatts here.
...
- 2,184
7
votes
Accepted
How do I protect the power supply from a short circuit inside a device?
A simple way to address this is to use a polyfuse inside your device. These work by detecting an overcurrent condition, then 'tripping' to limit the current to a lower value until the power is removed,...
- 56k
7
votes
How can I make an alarm circuit which senses both cutting and shorting the wire?
The thing you’re asking about is called in the trade a ‘supervised loop’. This can be implemented using a known load at the end of the line, such as a resistor or a Zener diode as well as other anti-...
- 56k
6
votes
How do I protect the power supply from a short circuit inside a device?
Put a fuse inside the device you are designing.
You know the power and the voltage and current so select a suitable fuse with sufficient headroom and fast or slow blow as applicable.
- 6,549
6
votes
Accepted
ESP32 and security
See also Marcus Müller's answer for important additional views
Telnet is of course not secure at all, in that it provides no encryption or other security features; it appears your design is intended ...
- 15.2k
6
votes
Switch ELECTRICALLY SAFE between 3 resistive loads (16 A each) on a 16 A line
Suggestion #3 - hardware logic drives the contactors so that only a maximum of one switch is driven, regardless of the code sent to it by the MCU. For instance, use a 74HC138 or 139 to decode 2 binary ...
- 171k
5
votes
Is it possible to jam wireless home alarm systems?
Yes, it is possible to jam wireless alarm systems, probably even with low-cost, low-tech DIY devices (google "broadband jamming DIY"). There are a couple of articles online which report successful ...
5
votes
electric bedroom heated mattress vs danger
I am assuming that the heating device is an "electric blanket" used on top of a mattress.
Such blankets MUST NOT be used underneath a mattress as they can then cause fires.
If this is NOT an electric ...
- 151k
5
votes
Reverse engineer this old burglar alarm panel
Here is the datasheet for the 7220:
https://lsicsi.com/datasheets/LS7220.pdf
It looks like the grey wire is common to all of the switches and the whitе wire is common to all of the diodes. The diodes ...
- 22k
4
votes
What security risks does the Test Access Port (TAP) introduce?
First, you're under the false impression that SW debugging mechanisms get removed from final products. For example check Windows debugging API: it has broad potential for abuse (reading other ...
- 26k
4
votes
Accepted
What security risks does the Test Access Port (TAP) introduce?
Yes, TAP introduces hardware security risks. If you have access to the JTAG port you may be able to introduce false input/output. However many chips provide a JTAG disable configuration that disables ...
- 20.6k
4
votes
Accepted
Is CDMA more secure than LTE or GSM?
LTE (and GSM I believe) uses OFDM (orthogonal frequency division multiplexing) and simulataneously transmits several different "carriers" each containing a fraction of the full data bits. Upon ...
- 467k
4
votes
Blow MSP430 security fuse with FET430 or MSP-FETFlash programmer
Actually only 2 TI programmers can blow fuses (electrical and software fuses) on the MSP430 MCU line:
MSP-FET430UIF (the white box, mini USB)
and
MSP-FET (the black box, micro USB)
As per document: ...
- 69
4
votes
Accepted
Wireless or wired solution for perimeter fence security?
To be clear I don't understand wireless the ways the engineers here do, and that may be the best option for you. When you're evaluating wireless though, take into account battery cost, effect of ...
- 4,143
4
votes
Is POR Secure Memory/peripherals on ARM common in real hardware just a feature of QEMU?
I am less familiar with the software side of things or QEMU, but I have dropped a number of ARM cores on silicon.
It is possible in hardware to check the AXI bus protection bits ...
- 14.5k
4
votes
What is the ideal method of sensing whether 4 points on the bottom of a device are all depressed to indicate contact?
An near-infrared LED can be paired with a phototransistor. They will work behind a plastic panel or inside a plastic foot or or potted in an epoxy foot. And most common plastics and epoxies are ...
- 57k
Only top scored, non community-wiki answers of a minimum length are eligible