OHS is open source based burglar alarm and automation platform. It can work as new alarm gateway, or it can replace your old alarm panel. OHS can use any wired 12V sensor, PIR, smoke or reed switch. It has Web interface that is used to set it up. OHS has GSM modem that is able to send SMS or page you. It has radio interface for environmental sensors. OHS is self-contained, it does not need any cloud service, only optional SMTP server for emails, or MQTT server to publish collected sensor data.
Thank you, Adam. OHS is very interesting to me, in particular I liked the balanced-input section. Some notes: in my opinion 0,2A for F2 is a little small because a single MW/IR sensor draws from 25 to 70mA or more. In my security system I plan to need at least 6 sensors (balanced inputs) so, as is, this number would certainly overload the 12V power pin. Not only: having a single, common supply, if one of the devices goes fried and in a short-circuit-condition it would KO the whole system ! I think that in the next version you could add multiple 12V sensor-supply pins (with resettable fuse to each rail not passing trough F1). To overcome the problem the owners of the current version should supply groups of sensors via the general power supply using suitable separate fuses. Do you plan to release in the future a new version of the gateway (e.g. 1.7D) ? Last but not least, I think that the availability of an RS485 expansion board to increase the number of balanced and digital inputs (or even outputs) would be very useful in order to expand the system and optimize the cabling. To do this you could probably simply clone the gateway excluding the SMS and IP sections. I hope my opinions can be useful to you.
thanks for your comments, I appreciate it. My PIRs are max 35mA with LED and 10mA without LED, and my calculation were with this in mind. But replacing F2 higher 0.4A fuse should be possible even in this version. I think the traces are wide enough (0.762mm) to carry higher current. And power supply I use along with battery is strong enough(35w@12V). But still good suggestion for next version I will keep it in mind.
What exactly do you mean by multiple 12V sensor pins? Gateway now have 4 groups of 12V rail with separate fuses connecting to one 0.65A fuse. Then the logic(GSM, Eth, MCU) has its own 0.65A fuse as well. I have tested the condition of having shorted 12V to ground on balanced sensors and the system worked fine just reporting "tamper" on all balanced inputs. You have some improvements in mind?
Expanding the inputs is possible. In software there is already defined RS485 and wireless expansion of balanced or unbalanced inputs. And it is working for both. There is even an option to have battery powered PIR with not periodic updates, sleeping between PIR. I plan to have blog post on this as I have it fully tested and I will publish example code for it.
Anther way is to use the I2C expansion connector. There is possibility of adding another 4x8 balanced or unbalanced inputs, but hardware for it is not ready as I did not needed. Basically it would be the part of unbalanced sensors together with I2C 8 channel ADC.
There will be future version for sure, one similar to existing one 1.8 maybe. And in future I'm leaning toward STM32F407 a 32 bit ARM, not because Atmel 1284P is not sufficient to handle existing tasks, but I would like to support SSL/TLS for HTTP and other Ethernet connections and 8Bit MCU is simply not able to handle encryption. But this is huge workload.
Hi, as there is no thread in the forum I ask here. Could you please explain the purpose of the 120R and the 1k resistor in the PIR sensor input? Thanks!
Sorry my question might be not specific enough. As you just said the series resistor for sure is limiting the current. However I am not sure why two resistor is needed instead of one. I can’t imagine how a current could be injected other than from the input pin. Many thanks for your reply!
The 1.6k already limits the current and the BAT device limit the voltage. Not sure why further protection is needed. I will do some spice simulation on it. Let me know if you are interested about the result.
Hi,
ReplyDeleteI'm sorry that I cant find your schematics, How do I for seeing your shematics?
Thank you.
Hello, now there is link to google drive folder.
DeleteHello Adam, can you please publish the BOM for the 1.7 ? Thank you very much.
DeleteHello Giovanni,
DeleteI will do it next week. Most recent variant I sell is 1.7C. I will publish BOM and schematics for this one.
OK, added.
DeleteThank you, Adam. OHS is very interesting to me, in particular I liked the balanced-input section. Some notes: in my opinion 0,2A for F2 is a little small because a single MW/IR sensor draws from 25 to 70mA or more. In my security system I plan to need at least 6 sensors (balanced inputs) so, as is, this number would certainly overload the 12V power pin. Not only: having a single, common supply, if one of the devices goes fried and in a short-circuit-condition it would KO the whole system ! I think that in the next version you could add multiple 12V sensor-supply pins (with resettable fuse to each rail not passing trough F1). To overcome the problem the owners of the current version should supply groups of sensors via the general power supply using suitable separate fuses. Do you plan to release in the future a new version of the gateway (e.g. 1.7D) ? Last but not least, I think that the availability of an RS485 expansion board to increase the number of balanced and digital inputs (or even outputs) would be very useful in order to expand the system and optimize the cabling. To do this you could probably simply clone the gateway excluding the SMS and IP sections. I hope my opinions can be useful to you.
DeleteHello Giovanni,
Deletethanks for your comments, I appreciate it. My PIRs are max 35mA with LED and 10mA without LED, and my calculation were with this in mind. But replacing F2 higher 0.4A fuse should be possible even in this version. I think the traces are wide enough (0.762mm) to carry higher current. And power supply I use along with battery is strong enough(35w@12V). But still good suggestion for next version I will keep it in mind.
What exactly do you mean by multiple 12V sensor pins? Gateway now have 4 groups of 12V rail with separate fuses connecting to one 0.65A fuse. Then the logic(GSM, Eth, MCU) has its own 0.65A fuse as well. I have tested the condition of having shorted 12V to ground on balanced sensors and the system worked fine just reporting "tamper" on all balanced inputs. You have some improvements in mind?
Expanding the inputs is possible. In software there is already defined RS485 and wireless expansion of balanced or unbalanced inputs. And it is working for both. There is even an option to have battery powered PIR with not periodic updates, sleeping between PIR. I plan to have blog post on this as I have it fully tested and I will publish example code for it.
Anther way is to use the I2C expansion connector. There is possibility of adding another 4x8 balanced or unbalanced inputs, but hardware for it is not ready as I did not needed. Basically it would be the part of unbalanced sensors together with I2C 8 channel ADC.
There will be future version for sure, one similar to existing one 1.8 maybe. And in future I'm leaning toward STM32F407 a 32 bit ARM, not because Atmel 1284P is not sufficient to handle existing tasks, but I would like to support SSL/TLS for HTTP and other Ethernet connections and 8Bit MCU is simply not able to handle encryption. But this is huge workload.
Hi, as there is no thread in the forum I ask here. Could you please explain the purpose of the 120R and the 1k resistor in the PIR sensor input? Thanks!
ReplyDeleteHello, they limit the current.
DeleteSorry my question might be not specific enough. As you just said the series resistor for sure is limiting the current. However I am not sure why two resistor is needed instead of one. I can’t imagine how a current could be injected other than from the input pin.
DeleteMany thanks for your reply!
It is to further limit the current flowing to uC which is left after clamping to the sink circuit.
DeleteThe 1.6k already limits the current and the BAT device limit the voltage. Not sure why further protection is needed. I will do some spice simulation on it. Let me know if you are interested about the result.
ReplyDeleteSure, let me know. My intention was to protect the uC clamping circuit from over voltage or negative voltage.
Delete